And its moment

arm will be one half of 16, or eight.

because this total side is 16, equals 0.

And once you've done that

you can solve for WA, and in

this case WA ends up equaling

12 pounds for impending tipping

down the plane. 'Kay, so now let's do a little thought

experiment, here. Let's say that WA, here, is 20 pounds.

And we want to look at impending motion down the plane.

And, at 20 pounds, we're going to assume that it's in static equilibrium.

As I lower the

weight, once I get to 18

pounds, the block B is going to slide down the plane.

We'll never get to the level of 12 pounds, where it

will tip down the plane, because it will already have slid first.

And so therefore, WA must be greater than or equal to 18

pounds to, for static equilibrium,