my question is given the interval 2 is less than or equal to x which is less than or equal to 10; find the midpoint of a the line y = 4x+8

the midpoint x is given by
x=1/2 (2+10)=6

what is y when x=6?

THAT IS HARD CUZ I'M JUST IN ALGEBRA I AND WE HAVEN'T LEARNED THAT YET OR MAYBE I JUST WASN'T LISTENING. SORRY!!!

How do you find the midpoint of 5 and 7