Solution

Equal lot

let’s say he bought 35 in each lot. 

in first lot 35 for 5 Rs. 

and in second lot 35 for 7 Rs. 

so total 70 for 12 Rs.

he then sold 40 for 12 Rs.

Hence his profit is 30 apples over 40 apples

= 30/40*100 = 75%