The area of a rectangle is 64 square centimeters. the rectangle is 4 centimeters wide. how long is the rectangle.

The Area is the width times the height: A = w x h;
Then, 64 = w x h;
h = 4 + w;
64 = 4w  + w^2;
w^2 + 4w - 64 = 0;
We solve this equation: w1 ≈ 6,24 > 0 (okay); w2 ≈ - 10,24 < 0 (not okay);
Finally, h1 ≈ 10,24;