From symmetry, if it contains the point (2,0), which is (5-3, 0), then it also contains the point (5+3, 0) or (8, 0). Hence you have three equations:
From (2, 0): 0 = a*22 + b*2 + c
From (5,3): 3 = a*52 + b*5 + c
From (8, 0): 0 = a*82 + b*8 + c
Use these three equations to find a, b and c.