    #### 1.   If 20 + y = 42, solve y

The inverse of 20 is − 20. So subtract 20 from both sides

 20 + y = 42 − 20 = − 20

 y = 22

To verify, put the value of y = 22 back into the original equation
20 + 22 = 42

#### 2.   If 6 + z = 15, solve z

The inverse of 6 is − 6. So subtract 6 from both sides

 6 + z = 15 − 6 = − 6

 z = 9

To check, put the value of z = 9 back into the original equation
6 + 9 = 15

#### 3.   If 7 + t = 35, what is value of t?

The inverse of 7 is − 7. So subtract 7 from both sides

 7 + t = 35 − 7 = − 7

 t = 28

To verify, put the value of t = 28 back into the original equation
7 + 28 = 35

#### 4.   If 9 + z = 7, solve z

The inverse of 9 is − 9. So subtract 9 from both sides

 9 + z = 7 − 9 = − 9

 z = −2

To check, put the value of z = −2 back into the original equation
9 + (−2) = 9 − 2 = 7

#### 5.   If x − 15 = 7, what is value of x?

The inverse of − 15 is + 15. So add 15 to both sides

 x − 15 = 7 + 15 = + 15

 x = 22

To verify, put the value of x = 22 back into the original equation
22 − 15 = 7

#### 6.   If y − 120 = 4, solve y

The inverse of − 120 is + 120. So add 120 to both sides

 y − 120 = 4 + 120 = + 120

 y = 124

To check, put the value of y = 120 back into the original equation
124 − 120 = 4

#### 7.   If z − 10 = −5, what is value of z?

The inverse of − 10 is + 10. So add 10 to both sides

 z − 10 = − 5 + 10 = + 10

 z = 5

To verify, put the value of z = 5 back into the original equation
5 − 10 = −5

#### 8.   If a − 25 = −38, solve a

The inverse of − 25 is + 25. So add 25 to both sides

 a − 25 = − 38 + 25 = + 25

 a = − 13

To check, put the value of a = −13 back into the original equation
−13 − 25 = −38

#### 9.   If 17 + b = −5, what is value of b?

The inverse of 17 is − 17. So subtract 17 from both sides

 17 + b = − 5 − 17 = − 17

 b = −22

To verify, put the value of b = − 22 back into the original equation
17 + ( − 22 ) = 17 − 22 = −5

#### 10.   If c + 20 = −34, solve c

The inverse of 20 is − 20. So subtract 20 from both sides

 c + 20 = −34 − 20 = −20

 c = −54

To check, put the value of c = −54 back into the original equation
−54 + 20 = −34 back to:   