solve for x and y in the following system of equations. y=3x^2+8x-10 & y=x^2+7x+5

how do you do this ?

It would be the same way as you would do for linear simultaneous equations:

eliminate one of the variables. In this case, y is easy to eliminate.
3x^2+8x-10 = y = x^2+7x+5
Solve the resulting quadratic equation to get x=5/2 or x=-3.

As a check, substitute each of these values into the original equations to see if the values of y are equal.