Answer:
x = -1
Step-by-step explanation:
[tex]Midpoint =(1,2)= (x,y)\\J(3,-3)=(x_1,y_1) \:and\:K(x,7)= (x_2,y_2)\\\\x = \frac{x_1+x_2}{2} \\\\1 = \frac{3+x}{2}\\ \\Cross\:Multiply \\2\times 1 = 3+x\\2 =3+x\\2-3=x\\-1=x\\\\x =-1[/tex]
