Answer
a) $P=d\sqrt d$
d) $11.86$ Earth years
Work Step by Step
$$P=\sqrt{d^3}$$
a) Simplify:
$$P=\sqrt{d^2\cdot d}=\sqrt{d^2}\cdot\sqrt {d}=|d|\sqrt{d}=d\sqrt d$$
because $d\geq 0$.
b) Find $P$ when $d=5.2$:
$$P=5.2\sqrt{5.2}\approx11.86~~\text{Earth years}$$
