Answer
$T=1.23s$, $f=0.813$ Hz
Work Step by Step
Use dimensional analysis to find the time it takes for one heart beat. $$\frac{74 beats}{1min} \times \frac{1min}{60s}=1.23s$$ This is the period. To find frequency, use the formula relating period with frequency, which is $$f=\frac{1}{T}$$ Substituting the known value of $T=1.23s$ yields a frequency of $$f=\frac{1}{1.23s}=0.813Hz$$