This is a directional hypothesis test. The bank claims P = 0.40, but the sample data = 170/500 = 0.34.
Ho: P = 0.40
Ha: P < 0.40
Z = (p - P) / Sp
"small" p = 0.34
"big" P = 0.40
Sp = sqrt(P*q/n) --> q = 1 - P = 0.6, n = 500
Once you find Z, determine its probability in the normal distribution tables (this is the p-value).
If it's really small (say < .05), you have enough evidence to reject the bank's claim.