Suppose You Wanted to Determine If You Should Reject the Null

Suppose you wanted to determine if you should reject the null hypothesis that running a playing fast tempo (as opposed to slow) music in your store has no effect on sales. On 65 randomly selected days with fast tempo music on the average store sales is $2,345 with a sample standard deviation of 45, while on 75 randomly selected days with slow tempo music on the average store sales is $2,555, with a sample standard deviation of 65. What would be the proper t-stat for this hypothesis test?

A) $\frac { 2345 - 2555 } { \sqrt { \frac { 45 ^ { 2 } } { 65 } + \frac { 65 ^ { 2 } } { 75 } } }$
B) $\frac { 2345 } { \sqrt { \frac { 45 ^ { 2 } } { 65 } + \frac { 65 ^ { 2 } } { 75 } } }$
C) $\frac { 2345 - 2555 } { \sqrt { \frac { 45 } { 65 } + \frac { 65 } { 75 } } }$
D) $\frac { 2345 - 2555 } { \sqrt { 45 ^ { 2 } + 65 ^ { 2 } } }$