In each case, you can use the second equation to create an expression for y that will substitute into the first equation. Then you can write the result in standard form and use any of several means to find the number of solutions.
System A
x² + (-x/2)² = 17
x² = 17/(5/4) = 13.6
x = ±√13.6 . . . . 2 real solutions
System B
-6x +5 = x² -7x +10
x² -x +5 = 0
The discriminant is ...
D = (-1)²-4(1)(5) = -20 . . . . 0 real solutions
System C
y = 8x +17 = -2x² +9
2x² +8x +8 = 0
2(x+2)² = 0
x = -2 . . . . 1 real solution
