Let x be the width, and y be the length.
We know that y = 2x+1 (the length is 1ft more than double the width).
We know that x * y = 45 (length times width = area)
This gives us a system of equations. If we substitute 2x+1 in the place of y in the second equation, we get x * (2x+1) = 45.
Doing the multiplication on the left side gives us 2x^2 + x = 45.
Subtracting 45 from both sides yields 2x^2 + x - 45 = 0.
This is a polynomial equation and can be solved using any of the various methods (factoring, quadratic formula, etc). The solutions are x = 0, x = 9/2. Since x represents the width, it cannot be 0, so it must be 9/2.
Plugging that back in to the original y = 2x+1, we get y = 2(9/2)+1. Solving that shows that y = 10.
So the width is 9/2 in, and the length is 10 in. If you plug these back into the original question, you will see that they satisfy the requirements.