Let M be Marion, L be Lori and E be Elijah.
M = 3.5 ft.
E = M - 4/12 (since he was 4 inches shorter than Marion) = 3 1/2 - 4/12; find a common denominator (12): 3 6/12 - 4/12 = 3 2/12 = 3 1/6 ft.
L = M + 1.25 (since she was 1 1/4 feet taller than Marion) = 3.5 + 1.25 = 4.75 feet.