The area is 30 square centimeters and a height with 10 centimeters. What is the length of the base?

So,

The formula for the area of a rectangle is:

A = l * w

We will consider l to be the height.

Substitute the given values.

30 = 10 * w or 10w

Divide both sides by 10.

3 = w

The length (I would call it the width, since it is shorter) of the rectangle is 3 centimeters.

30/10=3 3 cm is the length.