Alfie is 5 years old. His mother is 28. How old will Alfie be when he is exactly half as old as his mother?
Let x be the number of years until Alfie is half as old as his mom; then
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.