If The Facts Are H O Mu 275 Vs H A Mu 275 N 500 Df N 1 Or 499 Xbar 280 S 25 Calc

If the facts are: 

Ho: mu = 275 vs Ha: mu > 275

N = 500

df = n-1 or 499

Xbar =280

S = 25

Calculated test statistic is 4.47

If asked to supposes the test statistic was 2.67 how would one calculate the associated p-value?

Am I using the Student’s t Table and calculating for a one-sided p value or some other procedure and table?