Answer:
16b + 13z
Explanation:
I am 100% sure its that answer.
add 7z and 6z, and you'll get 13z.
add 7b and 9b, and you'll get 16b.
We're not forgetting the plus sign in the middle, so 16b + 13z is your answer.
Option D
7b + 7z +9b +6z
(7+9) b +(7+6)z
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