Answer:
HK = 20
Step-by-step explanation:
LM = (1/2) HK {Mid point theorem}
2*(10x - 90) = 10x - 80
2*10x - 2*90 = 10x - 80
20x - 180 = 10x - 80 {add 180 to both sides}
20x = 10x - 80 + 180
20x = 10x +100 {Subtract 10x from both sides from }
20x -10x = 100
10x = 100
x = 100/10
x = 10
HK = 10x - 80
= 10*10 - 80
= 100 - 80
= 20