Answer:
174.8 guppies.g/week
Step-by-step explanation:
B(t) = N(t)M(t)
Utilizing the product rule of derivative

Applying the rule to B(t) = N(t)M(t)

from the question
t=4 weeks, N(4) = 820 guppies
d(N(4))/dt = 50 guppies/week
m(4) = 1.2g
d(M(4))/dt = 0.14g/week
