$[$SOA $36$; SOA$-$IT$\mathrm{.}049]$ Happy and financially astute parents decide at the birth of their

daughter that they will need to provide $50,000$ at each of their daughter's $18$th$,19$th$,20$th

and $21$ st birthdays to fund her college education. They plan to contribute $x$ at each of

their daughter's $1$st through $17$th birthdays to fund the four $50,000$ withdrawals. They

anticipate earning a constant $5\%$ annual effective interest rate on their contributions.

Let $v=\frac{1}{1\mathrm{.}05}$

Determine which of the following equations of value can be used to calculate $x.$