Another way to solve this problem is to use logarithms.
log(100.48) = log(x) log(100.7) = log(y) and log(xz) = log(y2)
So: 0.48 = log(x) 0.7 = log(y) and z log(x) = 2 log(y)
Substituting: (0.48) z = (0.7)(2) ==> z = 35/12
Correct answer is: (a) 2 11/12