Answer
$a) 73 $ boxes
$b)4 $ trips
Work Step by Step
a) $50x+210+95\leq4000$
210+95=305: $50x+305\leq4000$
4000-305= 3695: $50x\leq3695$
Divide both sides by 50: $\frac{50x}{50}=\frac{3695}{50}$
Simplify: $x\leq73.9$
b) Divide 275 by 73: $\frac{275}{75}\approx3.8$
This means that he can make 3 trips with a full load, and the 4th trip has to be less than full.
4 trips
