this means alternate interior angle are congruent. to solve this, you would equal them together.
you would write out the equation, and then subtract 6x on both sides.
7x-7 = 6x+11
-6x -6x
this will give you
1x-7 = 11
you then add 7 on both sides
1x - 7 = 11
+ 7 +7
1x = 18
divide by 1 to solve for x
1x÷ 1
18÷ 1
x=18