11%
The main issue when determining the percent error in a measure measurement is determine what to divide by. Do you divide the error by the measured value, or do you divide by the correct value? The convention is to divide by the correct value. So take the measured value minus the correct value and then divide by the correct value to get the percent error. So:
(7.2 - 6.5)/6.5 = 0.7/6.5 = 0.107692308 = 11% error
