Answer
The initial charge on sphere A is $~~+16e$
Work Step by Step
Let $q$ be the initial charge on sphere A.
After sphere W touches sphere A, the charge on each of sphere A and sphere W is $\frac{q}{2}$
After sphere W touches sphere B, the charge on each of sphere B and sphere W is $\frac{\frac{q}{2}-32e}{2} = \frac{q}{4}-16e$
After sphere W touches sphere C, the charge on each of sphere C and sphere W is $\frac{\frac{q}{4}-16e+48e}{2} = \frac{q}{8}+16e$
We can find $q$:
$\frac{q}{8}+16e = +18e$
$\frac{q}{8} = +2e$
$q = +16e$
The initial charge on sphere A is $~~+16e$
