Question 1178274
 90% certain:  z = 1.645
{{{z =blue (x - mu)/blue(sigma/sqrt(n)) = ME* sqrt(n)/blue(sigma) }}}     
0r
{{{ n = ( z*sigma/ME)^2 = (1.645*sigma/(sigma/2))^2  = 2.706*4 = 10.8241}}}
n = 11  (rounding up to next whole number)