A sum of money at simple interest amounts to 815 in 3 years and to 854 in 4 years. The sum is:

Step-by-step explanation:

So the amount after 4 yrs = amount after 3 yrs plus interest for 1 year;

one year =854-815=39 rate of simple interest;

so 3 yrs x 39 simple interest = 117;

so 815-117 = 698

the sum is 698

x/3-10=8

x/3=18

x=48