Solve the following equation by transforming it into a perfect square trinomial. x2 – 4x = 5 will mark as brilliant

Anyone know? will mark brainliest if correct!

Can someone answer this question? : )

The fence around a quadrilateral-shaped pasture is 3a^2+15a+9 long. three sides of the fence have the following lengths: 5a, 10a-2, a^2-7. what is the length of the fourth side of the fence?