Question
I have a yard in the shape of a right triangle. The base is 37ft and the straight side is 81ft and the side at an angle is 89ft. I am needing top soil for it and am having trouble figuring the squared yard i need.

Answer
Ahh!! A math question.  Instead of looking at it as a triangle, look at it as HALF of a rectangle. (BTW, I checked your measurements and indeed, it is a true right triangle)

Since school is not in session in most areas right now, my fear that I'm doing your math homework for you is low.  That said, lets do some math:

So, if one leg of the rectangle is 37 and the other is 81, therefore the area equals 1/2 of 37' x81', or 1/2(2,997') = 1,498.5 square feet.

To get cubic feet or yards, figure the depth of topsoil you wish to add.  Generally, if you're just putting in lawn, we use 4" under our sod installations.  If you are going to plant in it, I'd go deeper by and inch or two.

At 4" deep, it is 1498.5 x 0.33' (that's 4"/12") = 499.5 cubic feet

To get yards, 1 cubic yard equals 27 cubic feet, so for our 4" topsoil, it is 499.5/27 = 18 1/2 cubic yards.  

Sounds like a lot, but your backyard is the size of most houses in our area.  Imagine filling the rooms of a house 4-inches deep with dirt!!

This is about as much as a tandem (those ones with the smaller trailer they pull behind...) dump truck can handle in one load.

If you go with only 3" deep, then the math is (1498.5'x 0.25')/27 = 13 7/8, or 14 cubic yards (they usually only sell full or half yards).

For every 1" depth, you'll have to buy 4.6 cubic yards, therefore, if you're generous, and want 6" deep, then expect to buy almost 28 cubic yards!!

In our area, topsoil goes for $17-$27/yard, depending on amount, special handling (like adding manure) and delivery distance.  

Have fun creating your Oasis!!

-Marc