A department store has determined that 25% of all their sales are credit sales. A random sample of 75 sales is selected and the proportion of credit sales in the sample is computed.

a) What is the probability that the sample proportion will be greater than 0.34?

my answer is:

n=75 p=0.25

mu=np=18.75

sigma=sqrt(n*p*(1-p)) = 3/75

0.34 * 75=25.5

z=x-mu/sigma = 25.5-18.75/3.75 =1.8

P(z>1.8)=0.0359

the answer i got is 0.0359 but i am not confident, please tell me if i am correct or not. Thanks.