The school board is interested in the proportion of middle s

The school board is interested in the proportion of middle school students who do not live with both biological parents. How many students will need to be surveyed so that the board can be 90% confident in the results, with no more than 5% error?

Need step by step please.

Compute Sample Size ( n ) = n=(Z/E)^2*p*(1-p)
Z a/2 at 0.1 is = 1.64
Samle Proportion = 0.5
ME = 0.05
n = ( 1.64 / 0.05 )^2 * 0.5*0.5
= 268.96 ~ 269