Find two numbers, if their sum is 3/5 and their difference is 7 1/5

Set up a system of equations:

x + y = 0.6
x - y = 7.2

You can solve using elimination. Add the two equations together:

2x + 0y = 7.8
2x = 7.8
x = 3.9

Then plug the number back into either of the two original equations to solve for y:

3.9 + y = 0.6
y = -3.3

The two numbers are 3.9 and -3.3

The american colonies would have been ruled by a king.