The equation of line a is y = 7x + 12. line b is perpendicular to line a and passes through the point . what would be the solution to the system of equations represented by line a and line b?

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 :)