Tell whether the ordered pair (-3,5) is a solution of the system

It is a solution to the system. The best way to tell this is to try the ordered pair in each of the equations. 

2x - 3y = -21
2(-3) - 3(5) = -21
-6 - 15 = -21
-21 = -21 (TRUE)

3x - y = -14
3(-3) - (5) = -14
- 9 - 5 = -14
-14 = -14 (TRUE)

Since both equations come out true, it must be a solution. 

Cookies: 20 Brownies: 30

Step-by-step explanation:

That is a ratio, we can say she baked 20 cookies and 30 brownies