1) Thirteen plus the product of 6 and a number is 67.
13 + 6x = 67 ; where x is the unknown number.
6x = 67 - 13
6x = 54
6x/6 = 54/6
x = 9
13 + 6(9) = 67
13 + 54 = 67
67 = 67
2) negative 8 minus the product of 3 and a number is 19
-8 - 3x = 19 ; where x is the unknown number
- 3x = 19 + 8
- 3x = 27
-3x/-3 = 27/-3
x = -9
-8 - 3(-9) = 19
-8 + 27 = 19
19 = 19
