Which of these expressions are correct variations of the combined gas law?

The combines law of gas is:

P1 * V1     P2 * V2
=
    T1           T2

So, you can obtain many equivalent valid forms depending on the variable that you solve for.

These are some examples:

Solve for T1:

T1 = T2 * (P1 * V1) / (P2 * V2)

Solve for V2:

V2 = V1 * (T2 / T1) * (P1 / P2)

Solve for P1:

P1 = P2 * (T1 / T2) * ( V2 / V1)

The use of piers and beams to build a strong foundation for a house.

8.7 degrees celsius and 15.6 degrees fahrenheit