Answer:
Let the price of one book be Rs. x
price of next book is = 1040 - X
C.P of 1st book is Rs. x
Loss = 15%
S.P of 1st book = 85x / 100
C.P of 2nd book = 1040 - X
Profit = 36%
S.P of 2nd book = (1040 - x × 136)/100
(85x)/ 100 - (1040 - x × 136) / 100
85 x= 1040 x 136 - 136 x
85 x + 136 x= 1040 × 136
221 x = 1040 x 136
X = (1040 x 136) / 221
X = 640
So, Cost price for 1st book is 640 Rs. and 2nd book is 1040 - 640 = 400 Rs.