By the substitution property of equality, substitute all x's with ¹/₂ and all y's with -5.
1. -2xy = -2(¹/₂)(-5) = 5
2. 4x² - 3y = 4(¹/₂)² - 3(-5) = 1 + 15 = 16
3. 10y/(12x + 4) = 10(5)/(12(¹/₂) + 4) = -50/10 = -5
4. 11x - 8(x - y) = 11(¹/₂) - 8(¹/₂ - -5) = ¹¹/₂ - 8(¹¹/₂) = -7(¹¹/₂) = -⁷⁷/₂ = -38.5
Substitute a's with -9 and b's with -4
5. 3ab = 3(-9)(-4) = 108
6. a² - 2(b + 12) = (-9)² - 2(-4 + 12) = 81 + 8 - 24 = 65
7. 4b²/(3b - 7) = 4(-4)²/(3(-4) - 7) = 64/-19
8. 7b² + 5(ab - 6) = 7(-4)² + 5((-9)(-4) - 6) = 112 + 150 = 262
9. x = 7.25, y = 3.25 --> 4x: people w/o popcorn, 2(x + y): people w/ popcorn; 4x + 2(x + y) = 4(7.25) + 2(7.25 + 3.25) = 29 + 21 = $50