Question 906157
as I can see on image, you have this

{{{E(n) =  (2/3)n - (1/60)n^2 }}}

For this problem, E(n) is a function of n. We're trying to find the maximum value of E(n). 

 Assuming this is for a pre-calculus or calculus course, they probably want you to take the derivative. 

 So the derivative is: 
 E'{{{(n) = 2/3 - (1/60)n}}}

 The maximum then occurs when {{{2/3 - (1/60) n = 0}}}. 
 So {{{ (1/60) n = 2/3}}}, and {{{n =(2/3)/(1/60)= 120/3}}} or {{{n = 40}}}.