This is an isosceles triangle, and so the two leg's will be congruent.
Place the two leg measurements equal to each other
6x = 3x + 9
Isolate the 9. Subtract 3x from both sides
6x (-3x) = 3x (-3x) + 9
6x - 3x = 9
3x = 9
Isolate the x. Divide 3 from both sides
3x/3 = 9/3
x = 9/3
x = 3
3, or B) is your answer
hope this helps
