Use the Five-Step Strategy for Solving Word Problems to Find $y _ { 1 } = \frac { 1 } { x + 2 } , y _ { 2 } = \frac { 1 } { x - 2 } , y _ { 3 } = \frac { 1 } { x ^ { 2 } - 4 }$

Multiple Choice

Use the five-step strategy for solving word problems to find the number or numbers described in the following
exercise.
- $y _ { 1 } = \frac { 1 } { x + 2 } , y _ { 2 } = \frac { 1 } { x - 2 } , y _ { 3 } = \frac { 1 } { x ^ { 2 } - 4 }$ , and the difference between 9 times $y _ { 1 }$ and 7 times $y _ { 2 }$ is the product of 10 and $y 3$ .

A) $\{ 21 \}$
B) $\{ - 21 \}$
C) $\{ \sqrt { 57 } \}$
D) $\{ 42 \}$