Standard Deviation Of The Distribution Of The Difference Between Means is known as standard error

t-score = (mean1-mean2)/ standard error

Here

mean 1 = 55

mean 2 = 51

Standard error=0.76 (square root of (6.5/15 + 4.5/23))

T-score = (55-51)/0.76

=4/0.76

t-score = (mean1-mean2)/ standard error

Here

mean 1 = 55

mean 2 = 51

Standard error=0.76 (square root of (6.5/15 + 4.5/23))

T-score = (55-51)/0.76

=4/0.76

**T-score =5.263 >>> answer**