Using four equations to solve a problem is called a four order system

The answer to your question would be true.

Similarly to fact that a two-order uses two equations, and a three-order system uses three, so a four-order uses four. Basically, just remember that the number of equations matches the number of the order.

So we need to solve:

3ˣ⁻¹ = 9ˣ⁺²

To do this, we need to have the same base for both sides of the equation.

So let's go with the base of 3.

3² = 9

3ˣ⁻¹ = (3²)ˣ⁺²

3ˣ⁻¹ = 3²ˣ⁺⁴

Since the bases are the same now, we need to get rid of them and we would get:

x - 1 = 2x + 4

Subtract both sides by 2x:

-x - 1 = 4

Add 1 to both sides:

-x = 5

Divide both sides by -1:

x = -5