Can someone help me with these two questions. Thanks a lot.

1. A zero order reaction has a consant rate of 5.0 * 10^-4 M/s. If after 65 sec. the concentration has dropped to 9.0 *10^-2, what was the initial concentration?

I did so far: 9.0 * 10^-2 = -(5.0 * 10^-4)(65) + x
x = .087 but this is wrong.

2. AB -> A + B
A Plot of 1/AB vs. time yields a straight line w/ slop 5.7 *10^-2 M s. If the initial concentration of AB is 0.220 M, and reaction mixture initially contains no products, what are concentration of A & B after 75 sec.

I did so far: 1/[A] = -(5.7 * 10^-2)(75) = 1/.220
= -4.275 + 4.54
= .265 but this is wrong as well

Please help me. Thanks inadvance!