Question

Molly has 4x + $10 and Ron has 20 - 5 x dollars how much money do they have altogether and how much money does Molly have been Ron

Answer 1

1. Do the opposite of addition (subtraction)

$4x - 10 - (-5x + 20)$

2. Change this equation (-5x - 20) into a positive (5x + 20)

$4x - 10 + 5x - 20$

$9x - 10$

Answer 2

Subtract them, just like you added: 
4x + 10 - (-5x +20) 
The minus turns (-5x + 20) into the opposite, or 5x - 20 
4x + 10 + 5x - 20 
9x - 10
I really hope this helps.