Question

K is the midpoint of JL. If JK = 7x + 4 and KL = 12x - 21, what is the length of JL?

Answer 1

JL = KL
7x+4=12x-21
25 = 5x
x=5
JK = 39
KL = 39
JL = 78

Answer 2

midpoint means the segments beside it aer equal measure
therefor
JK=KL
7x+4=12x-21
minus 7x both sides
4=5x-21
add 21 both sides
25=5x
divide oth sides by 5
5=x

LJ=2(JK)=2(KL)
find either JK or KL

7x+4
7(5)+4
35+4
39=JK

double taht
39*2=78

JL=78 units