So we have:
To find the area of the entire figure we can simply find the areas of each individual subfigure.
For rectangle A we have that its area is given by:

For rectangle B:

Where side x is given by:

Then the surface of rectangle B is:

C is a triangle, the area of a triangle is given by its base (y) times its height (x) divided by two:

We need to find y using the length of the base of the total figure:

Now that we found y we can find the area of the triangle:

The total area is then:

So the total area is 84 square inches.