Question 357804
Let x = # of unit increase in the price. 
Then the revenue function is {{{R(x) = (50 + 3.75x)(1000-4x)}}}.
the vertex happens at x = 355/3, or 118.333...
Since positive integral values are acceptable only, either x = 118 or x = 119.  Direct substitution into the revenue function, and comparison of the resulting values results in x = 118 giving the higher revenue.