Recall that the simple interest is only effective over the principal amount. So, it doesn't take into account the generated interest.
So, in one year, the interest would be
[tex]300\cdot\frac{3.7}{100}=11.1[/tex]since we have 4 years, we will have
[tex]4\cdot11.1\text{ = 44.4}[/tex]of interest.
We add this to the principal, so we have
[tex]300+44.4=344.4[/tex]so in the end, the account would have 344.4