A surveyor, standing 40 ft from the base of a building, measures the angle of elevation to the top of the building to be 70 degrees. How accurately must the angle be measured for the percentage error in estimating the height of the building to be less than 5 percent?

I tried:

$\displaystyle \tan {70^ \circ } = \frac{h}

{{40}}

$

$\displaystyle h = 40(\tan {70^ \circ }) = 109.899

$

but I'm not sure where to go from here