Given y=-LN(a)/b, standard deviations of a,b, how do I find standard dev. of y? Do I start w/ s.d. of LN(a)...?

[bashful]

Please help! If I have the formula y=-LN(a)/b and I know the standard deviation of both a and b, how do I determine the standard deviation of y? Do I determine the standard deviation of LN(a) as SD(a)/a and add the SD of b in quadrature? Thanks in advance...