Enter both equations, using separate lines for each equation, and then press 'Solve'.  It is important to understand that anytime you are solving a system of equations you are answering the basic question "Do the graphs of these equations touch?". They may touch in one point (one solution), no points (no solutions) or an infinite number of points (i.e. the equations define the same line).

Your systems of equations identifies a single point, (4,-3).  You might also want to examine the Line Wizards available through Algebrator:

Windows: http://www.softmath.com/tr/alg51win-tr-en.exe

Mac: http://www.softmath.com/tr/alg51mac-tr-en.dmg

FInally, it is also worth noting the variables are case-sensitive, hence 'Y=x-7' should be entered as 'y=x-7'.