Answer:
t = -1.54.
Explanation:
The test statistic is:

In which X is the sample mean,
is the value tested at the null hypothesis,
is the standard deviation and n is the size of the sample.
H0:μ=54.5
This means that

Your sample consists of 48 subjects, with a mean of 54.1 and standard deviation of 1.8.
This means, respectively, that

Test statistic



The test statistic is t = -1.54.