First we do what's in the parentheses, which is 3Δ9 3Δ9 a case of aΔb when a < b since a=3 < b=9, so we use 2ab+5, and get 2(3)(9)+5 = 59 So we replace the (3Δ9) by 59 in (3Δ9)Δ5 and have 59Δ5 59Δ5 a case of aΔb when a ≥ b since a=59 ≥ b=5, so we use 2b-a, and get 2(5)-59 = 10-59 = -49. Edwin