Step-by-step explanation:
a.
[tex]y = k {r}^{2} [/tex]
[tex]7 = k {3}^{2} [/tex]
[tex]7 = 9k[/tex]
[tex]k \: = \frac{7}{9} [/tex]
[tex]y \: = \frac{7}{9} {r}^{2} [/tex]
b.
[tex]y \: = \frac{7}{9} \times {15}^{2} [/tex]
[tex]y = \frac{7}{9} \times 225[/tex]
y = 175
