7. in some places, a suspension bridge is the only passage over a river. the height of one such bridge, h, in metres, above the riverbed can be modelled by h = 0.005x^2 + 24.
a) how many zeros do you expect the relation to have? why?
b) if the area was flooded, how high could the water level rise before the bridge was no longer safe to use?

i have answered a) but i don't know how to do b). the book says the answer is 24m if that . any suggestions are appreciated.