Since B is perpendicular to A. We can say that the gradient of B will be -1/7 (product of the gradients of 2 perpendicular lines has to be -1). Now we know that the equation for B is y=-(1/7)x + c with c being the y intercept. Since the point isnt specified in the question, we could leave the equation like this. But if there is a given point that B passes through, just plug in the x and y values into their respective places and solve to find c. That should give you the equation for b. Now, to find the solution of x, we have 2 equations: 1) y=7x+12 2)y=-(1/7)x+c
In this simultaneous equation we see that y is equal to both the expressions. So, 7x+12=-(1/7)x+c
Now, since the value of c is not found, we cannot actually find the value of x, but if we would find c, we could also find x since it would only be a matter of rearranging the equation. And there you go, that is your solution :)
