5 ft = 5 * 12 in = 60 inches
Four consecutive even numbers are: x, x + 2, x + 4, x + 6
x + x + 2 + x + 4 + x + 6 = 60
4 x + 12 = 60
4 x = 60 - 12
4 x = 48
x = 48 : 4
x = 12
Answer:
Those shelves should be: 12, 14, 16 and 18 inches long.
Verification: 12 + 14 + 16 + 18 = 60 in = 5 ft.