b = 10
Explanation:
Let the unknown variable = b
difference of a number and 9 = b - 9
Twice the difference of a number and 9 = 2(b-9)
Twice the difference of a number and 9 is equal to 2:
2(b-9) = 2
Expand the bracket:
2×b - 2×9 = 2
2b - 18 = 2
Collect like terms by adding 18 to both sides:
2b - 18 + 18 = 2 + 18
2b = 20
Divide both sides by the coefficient of b
coefficient of b = 2
2b/2 = 20/2
b = 10
