Now you have to look for a standarized normal table and look
for which the value of z such that P(Z < z) = 1/3.
b) Here you just have to find the distribution of W = X - Y. It can be done
using the Jacobian method, for example.
c) From letter b) you know what is the distribution of W, so
its expectation value and variance are also known. The formula to
compute the expectation and variance of a uniform variable are easily
obtained and then you have two equations with two unkown variables a and b.
Solve the system.