6x^2+x-1=(2x+1)( ) whats the missing factor

The triangles are similar. what is the value of x? enter your answer in the box. x = two right triangles. the larger right triangle is labeled x on the longer leg, 12 on the shorter leg and 20 on the hypotenuse. the smaller triangle is labeled 4 on the longer leg, 3 on the shorter leg, and 5 on the hypotenuse.

Can someone explain to me how to do

Find the slope intercept form of (-3,6) and (3,-6)