The equation has two parts: 7.5x (where x is the number of hours you works) and 40 (a constant). $40 is the amount you has saved before you start work. You also make $7.50 for each hour you work.
The constant $40 makes this a bit tricky but it's really not once you understand what the equation is saying.
Work ⬇️⬇️⬇️
Find x (the amount saved after working) in the equation: y=7.5x+40
1. Subtract 40 from both sides.
y −40=7.5x
2. Divide both sides by 7.5.
y−40
_____. =x
7.5
3. Switch sides.
y-40
x = _____
7.5