David and eric each shot 6 arrows at the target shown. david shot 4 arrows into a and 2 into b. his score was 18 points. eric shot 3 into a and 3 into b. his score was 21 points. how many points were given in an arrow in b?

Lets write an equation for each guy's shots and score:
4A + 2B = 18
3A + 3B = 21
To solve we multiply the first equation by -3 and the second by 2:
-12A - 6B = -54
  6A + 6B = 42

-12A + 0 = -12
A = 1
to find B we substitute in the first equation:
4A + 2B = 18
4(1) + 2B = 18
4 + 2B = 18
2B = 14
B = 7
therefore there were given 7 points in an arrow in B

A

2x + 3y = -6

3x - 4y = -12

<=> 6x + 9y = -18

6x - 8y = -24

=> 17y = 6

2x + 3y = -6

<=> y = 6/17

x = -60/17

=> A