First, we have to set up a proportion.
3 a
____ = ______
4 387
Next, we cross multiply to get a simplified equation
3(387) = 4a
Next, we combine like terms by multiplying 3 and 387
1161=4a
Finally, we have to divide both sides by 4, to get our variable, a, alone.
a = 290.25
It says estimate, and I just solved the problem, but a good estimate would've been 300, as 3/4 of 400=300.
