Hi. I never solved a system of equations like this in a math class, but I think I know how to do it on a TI 89 Titanium.
First, I have a question about your second equation. It reads Is there supposed to be a after the ? If there is, here is how to do it on a TI 89.
You can solve this using the Simultaneous Equation Solver Flash App. (This can be downloaded for free from TI's website).
Then enter the coefficents of x and y like in the first screenshot, and finally hit F5 to solve. The answer screen is in the second screenshot.
If there is not supposed to be a in the second equation, you could just solve it for and then plug it in to the other equation using the substutition method. (All of this could be done on a calculator), or you could solve it as a system using the same method described above making the coefficent of y 0 and moving the term to the other side of the equation.