Does anyone know what equation should be used?

When using the linear combination metho e linear combination method to solve a system of linear equations, the four options are:

Let f(x) = 3 − x . find the average rate of change of f(x) from x = a to x = a + h and simplify your answer so that no single factor of h is left in the denominator.

In the triangles, bc =de and ac fe.if the mzc is greater than the mze, then ab isdfelth