Using substitution which number from the set 15, 25, 35, 55 makes the equation y + 15 = 40 true

To find the number that makes the equation true, we can substitute each number from the given set into the equation and solve for y.

1. If we substitute 15 into the equation:
y + 15 = 40
15 + 15 = 40
30 = 40
Since 30 is not equal to 40, 15 does not make the equation true.

2. If we substitute 25 into the equation:
y + 15 = 40
25 + 15 = 40
40 = 40
Since 40 is equal to 40, 25 makes the equation true.

3. If we substitute 35 into the equation:
y + 15 = 40
35 + 15 = 40
50 = 40
Since 50 is not equal to 40, 35 does not make the equation true.

4. If we substitute 55 into the equation:
y + 15 = 40
55 + 15 = 40
70 = 40
Since 70 is not equal to 40, 55 does not make the equation true.

Therefore, the number from the set that makes the equation true is 25.