The error is actually pessimistic. If you're an I.B. or A-level student, you could just say that the fractional or relative error on the volume is three times the fractional error on the radius, which does indeed give 170cm^3. Doing it properly, one "sums the fractional errors in quadrature". -Square the fractional error on r, multiply by three and root the result to get the fractional error in volume. -That gives on 98cm^3.
 Can haz JS math filter?