Answer:
x = 21
Step-by-step explanation:
corresponding sides in similar polygons are proportional:
set a proportion: BC/FK = CA/KJ => 18/6 = x/7 => x = 18 × 7 ÷ 6 = 21
17. 3ab + 8a
18. -6c + 6
19. 8x + 4
20. x - 3
21. 12x - 4
15
36
5(4)+16=20+16=36