Maths problem: how to do, thanks?

a. 
Suppose Nina gets $x as her pocket money each month
Money saved in each of Sep. & Oct.= (2/5)x
Money saved in Nov.= x-115

Total savings = 2(2/5)x + (x-115) = 155
(9/5)x -115 = 155
(9/5)x = 270
∴ x = $150

b. Amount she spent in Sep. = 150(3/5) =$90

c. 
%tage of her monthly pocket money spent in Nov.
= (115/150)*100%
= 230/3 %
= 76.67 %(to 2 dec. pl.)