If something is BIsected that means that it is cut in half. This also means that both halfs are equal to one another, so this means you can set them equal to each other in an equation.
You first have to solve for x, so you would set up an equation that looks like this...
11x-6 = 3x+42. Then just solve for x
-3 +6. -3 +6
8x=48
/8. /8
x=6
You can check your work by inserting the answer into x.
11(6)-6. =60
3(6)+42 =60