You're very close! The statement is about two forces being balanced, but it's not quite right to say they are "balanced when a system is in isostasy." Here's the correct way to phrase it:

Two forces are balanced in a system that is in isostasy.

Here's a breakdown:

* Isostasy is a state of equilibrium where the Earth's crust "floats" on the denser mantle below.

* The two forces involved are:

* Gravity: pulling the crust downwards.

* Buoyancy: the upward force exerted by the mantle, supporting the crust.

So, in a system in isostasy, these two opposing forces are balanced, resulting in a stable condition.

Think of it like an iceberg: the portion of the iceberg above the water is balanced by the portion below the water, which is supported by the buoyancy of the water.