Ben and Alyssa play a game in which they earn the same number of points for each goal and lose the same number of points for each penalty. Ben makes 7 goals and 2 penalties, ending the game with 21 points. Alyssa earns 10 goals and 8 penalties and ends the game with -6 points. How much does a penalty cost and how much does a goal give?

Each goal gives 5 points and a penalty costs 7 points.

Step-by-step explanation:

Let a penalty cost = x points

And a goal gives = y points

Ben makes 7 goals and 2 penalties ending the game with 21 points,

7y - 2x = 21 (1)

Alyssa makes 10 goals and 8 penalties ending the game with (-6) points,

10y - 8x = -6

5y - 4x = -3 (2)

Equation (1) multiplied by 2, then subtracted from equation (2),

(5y - 4x) - 2(7y - 2x) = -3 - 2(21)

5y - 4x - 14y + 4x = -3 - 42

-9y = -45

y = 5

From equation (1)

7(5) - 2x = 21

35 - 2x = 21

2x = 35 - 21

2x = 14

x = 7

Therefore, each goal gives 5 points and a penalty costs 7 points.