A person lent a certain sum of money at 5% per annum at simple interest and in 8 years the interest amounted to $420 less than the sum lent. What was the sum lent?  Choose the correct choice:
A) 500
B) 600
C) 700
D) 800
E) 900

Rationale: "p - 420 = ( p * 5 * 8 ) / 100 p = 700 the answer is c ."
Answer: C