Pardon the handwriting

Rather straightforward but ill bring you through. By letting the smaller number be x, the larger consecutive number will be x+1. Squaring both numbers and adding them will give you 761. Arrange and simplify and you will get the expression in the question.

For part b, you are finding for the smaller number, which is x. Since the expression you got previously was a quadratic equation, you can use the quadratic formula to find x.

Hope it helps!