Answer:
20
Explanation:
z + 4 = 3z
z - 3z = - 4
- 2z = - 4
z = - 4 / - 2
z = 2
3 - y = - 7
- y = - 7 - 3
- y = - 10
y = - 10
xy
= 2 * 10
= 20
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