#### Answer

The magnitude of the charge on each sphere is $8.2\times 10^{-8}~C$.

#### Work Step by Step

We can find the magnitude of the force on each sphere as:
$F = ma$
$F = (0.0010~kg)(150~m/s^2)$
$F = 0.15~N$
We can find the magnitude of the charge on each sphere as:
$F = \frac{k~q~q}{r^2}$
$q^2 = \frac{F~r^2}{k}$
$q = \sqrt{\frac{F}{k}}~r$
$q = \sqrt{\frac{0.15~N}{9.0\times 10^9~N~m^2/C^2}}~(0.020~m)$
$q = 8.2\times 10^{-8}~C$
The magnitude of the charge on each sphere is $8.2\times 10^{-8}~C$.