Solution

shopkeeper pays for 100gm and takes 130gms while buying.

and then shopkeer covers the money of 100 gm while selling 85 gms.

effectively in the whole transaction shopkeeper recovers his entire cost by selling only 85 gms. So he is still left with 45 gms.

so now the amount he gets by selling 45 gms would be his profit over his spending. (his spending is equal to the amount he gets by selling 85 gms)

45 gms is his profit over 85 gms

profit % = (45/85)*100 = 53%