Solution
Let x be the number of years until Alfie is half as old as his mom; then
5 + x = ½(28 + x), or 2(5 + x) = 28 + x
10 + 2x = 28 + x
x = 28 - 10 = 18.
In 18 more years Alfie will be half the age of his mother. Alfie will be 5 + 18 or 23. His mom will be 28 + 18 = 46.