A sum of money at simple interest amounts to $ 780 in 3 years and to $930 in 4 years. The sum is:  Select.
A) $153
B) $698
C) $330
D) $549
E) $675
C   $330   S.I. for 1 year = $(930 - 780)= 
<gadget id="calculator">(930 - 780)</gadget>
<output>150</output>
$150.   S.I. for 3 years= $(150 x 3) = $450.   Principal = $(780 - 450)= 
<gadget id="calculator">(780 - 450)</gadget>
<output>330</output>
$330.
<result>C</result>
A sum of money at simple interest amounts to $ 780 in 3 years and to $930 in 4 years. The sum is: