Solve the Problem $R$ Varies Directly As $x ^ { 2 }$

Multiple Choice

Solve the problem.
- $R$ varies directly as $x ^ { 2 }$ and inversely as $t$ when $R = 30$ when $x = 6$ and $t = 12$ . Find $R$ when $x = 7$ and $t = 9$ .

A) $R = \frac { 9 } { 490 }$
B) $R = \frac { 490 } { 9 }$
C) $R = \frac { 3 } { 140 }$
D) $R = \frac { 140 } { 3 }$