The bar model is showing you that the sum of the bars on top is equal to the bars on bottom. So,
(5 - x) + (5 - x) = 50
Remove brackets
5 - x + 5 - x = 50
Add up the terms to make it bestee
10 - 2x = 50
Subtract 10 from both sides
-2x = 40
Divide by -2 on both sides
x = -20 is your answer
