15 - t + 8t = - 13

4a + 11 - a = 2

15-t + 8t = - 13

15 + 7t = - 13

7t = - 13-15

7t = - 28

t = - 4

4a + 11-a = 2

3a = 2-11

3a = - 9

a = - 3

Remember you can do anything to an equation as long as you do it to both sides

15-1t+8t=-13

15+7t=-13

minus 15 both sides

7t=-28

divide both sides by 7

t=-4

4a+11-1a=2

3a+11=2

minus 11 both sides

3a=-9

divide by 3 both sides

a=-3