Someone help, lol I've been tryna do the last too for so long, I think I am just tired...

Answer:
see explanation
Step-by-step explanation:
(a)
4 × 4 = 4²
(b)
5 × 5 × 5 × 5 = [tex]5^{4}[/tex]
(c)
3 × 7 × 7 × 7 × 7 = 3 × [tex]7^{4}[/tex]
(d)
2 × 9 × 9 × 9 × 2 × 9 ← rearrange
= 2 × 2 × 9 × 9 × 9 × 9
= 2² × [tex]9^{4}[/tex]