How many times Km must the substrate concentration be in order to achieve a velocity that is 90% of Vmax?

I need help in solving these biochemistry thanks. also attachment for all questions? 1. a. An alpha helix of 20-25 amino acids is needed to span the plasma membrane of cells. Based on the dimensions of an alpha-helix, calculate the range in width of the membrane? b. How many amino acids would be needed in an antiparallel beta strand to span the membrane? c. The maltose transporter maltoporin (Mr 49,913) spans the outer membrane of E. coli. It is comprised of 18 successive antiparallel β-strands arranged like the staves of a barrel to create a channel through the membrane. Beta-turns connect the strands on the periplasmic side of the membrane; loops connect the strands on the outer side. The N- and C-termini coincide with the ends of β-strands and are both on the periplasmic side. Calculate the average number of residues per outside loop? d. Given that the distance between Cαs of neighboring β-strands is 0.5 nm, what are the circumference and diameter of the β-barrel formed by the polypeptide backbone? Of course much of the interior of the barrel is occupied by side chains that narrow the channel and specify passage of only maltose and maltodextrins. e. Given that the width and thickness of maltose are about 0.5 nm, what percent of the diameter would the channel for maltose transport need to occupy? 2. For Michaelis-Menten phosphatase X with a Ks for substrate binding of 0.85 x 10-8 M, half maximal velocity is achieved with a substrate concentration of 0.35 μM. a. What kind of kinetics does this enzyme follow: rapid equilibrium or just the general steady state? Justify your answer. b. How many times larger is the catalytic rate constant than the reverse rate constant for substrate binding, k-1, by this phosphatase? c. How many times smaller is the catalytic rate constant than the rate constant for substrate binding, k1? d. How many times Km must the substrate concentration be in order to achieve a velocity that is 90% of Vmax? e. If the [E]total is increased 5 times in a reaction while [S] is left constant, how much greater will the initial velocity be?