Determine whether the ordered air is s solution of the given system of equations, remember to use alphabetical order of variables. (5,2); a+b=7 and 2a-8=b

Given your ordered pair you would assume a = 5, b = 2
Set up both equations 
5 + 2 = 7
7 = 7 (the numbers are equal so this correct)
2(5) - 8 = 2
10 - 8 = 2
2 = 2 (the numbers are equal so this is also correct)

Because both equations work with the ordered pair they are the solution of the given system.