There is nothing to solve for. You have specific inputs for p, er1, er2, and equation 3 has only those on the right hand side. Therefore the left hand side, ere, is completely defined as a specific numeric value.
Now take that numeric value for ere and substitute it and the p, er1, er2 into equation 2. The equation will either be satisfied or else it will not be.
Might I suggest that the real problem is to find the p value that works? If so then the solution is p = 1
With p = 0.27 then if you wanted to find one of er1 or er2 given the other, then the solution is er1 == er2