Geometry Problem help!?

E F G represent a mile marker along a straigh highway Find EF EF 6x-4 FG 3x the total of it is 5x+8 my brother said jsut solve for x by doing 6x-4 plus 3x and solve for x with 5x+8, he seemed rgumpy so i ddint wanna ask how i did that i know im an idiot i forgot Another one: J is the midpoint of HK find HJ JK and HK HJ 3x=5 JK 9x-3 Another: An angles meausre is 5 degress less then 3 times the meausre of its supplement. Find the measure of angle and the supplement