Suppose a speck of dust in an electrostatic precipitator has 1.0000×10121.0000×1012 protons

Suppose a speck of dust in an electrostatic precipitator has 1.0000×10121.0000×1012 protons in it and has a net charge of −5.00 nC (a very large charge for a small speck).

How many electrons does it have?