Our question transforms to finding the following sum : 3 + 7 + 11 + 15.... upto 15 terms
<span>Use formula for sum of an AP series </span>
<span>S = (n * (2a + (n - 1)d)) / 2 </span>
<span>n -> no of terms in AP series , so n = 15 </span> <span>a -> first term in series, so a = 3 </span> <span>d -> common difference, so d = 4 </span>
<span>Put all values for a, n, d and you will get the sum.</span>
