Answer:
Step-by-step explanation:
Let z and b represent the number of packs that Zack and Brian bought, respectively. Then the problem statement tells us ...
b = 2z -3 . . . . . . . Brian bought 3 fewer than twice what Zack bought
b + z = 30 . . . . . . they bought a total of 30 packs
Using the first equation to substitute into the second, we have ...
(2z -3) +z = 30
3z -3 = 30
3z = 33 . . . . . . add 3
z = 11
b = 2·11 -3 = 22 -3 = 19
_____
<em>Check</em>
b + z = 19 + 11 = 30 . . . . answer checks OK
Zack bought 11 packs; Brian bought 19 packs of gum.
