a) It looks like Revenue = Price * Quantity (Sound familiar to you? I have never seen this before....)
So Revenue = px
But p = -x/3 + 100
So R(x) = -x²/3 + 100x
b) It is saying 100 units are sold. So x = 100. You just put this into the equation that you just worked out.
R(100) = -100²/3 + 100x100 = 6667
c) To find out the maximum value the best way is to differentiate the equation and calculate dR/dx
dR/dx = -2x/3 + 100
Then set this equal to zero.
-2x/3 + 100 = 0
And you will find that x = 150
For the second part just put 150 back into the the forumla for R(x).
d) To see what price they need, just put the same value of x into the equation for p.