Answer:
I Believe you made an error on the perpendicular equation. It should be Y=-1/6x+6, as your original equation would be Y=6x-7. Perpendicular in simple terms means you flip it and change the sign, in this case 6 turns into -1/6. As for the B value (y=mx+b). I used point intercept,
Y - Y1 = M(X - X1)
Y - 6 = -1/6(X - 0)
Y - 6 = -1/6X
+6 +6
Y=-1/6x+6 There is you perpendicular equation, now erase the error you made and graph this. Also, your graph looks wrong.
As for your question of how to prove it, Plug your intersection back into the equation.
Explanation: