If the force experienced by a positively charged balloon is 2.7 newtons and the electric field strength is 7.8 * 105 newtons/coulomb, what is the magnitude of the charge on the balloon?

If you're careful about units, then you can do just about anything with

the two given quantities, and the answer will fall out on the desk right

there in front of you:

(2.7 newtons) / (7.8x 10⁵ newtons/coulomb)

Divide numerator

and denominator

by (newton), and

you have (2.7 coulomb) / (7.8 x 10⁵) = 3.46 x 10⁻⁶ coulomb

= 3.46 micro-coulombs

Notice that you didn't describe the direction of the force on the balloon, so

the flavor of the charge on it doesn't matter. A negatively charged balloon

with 3.46 microcoulombs on it would feel exactly the same force, but it would

be in the other direction.