Answer
$975$
Work Step by Step
Need to apply the summation formula for the arithmetic sequence, such as: $ \sum_{i=1}^{n}A=\dfrac{n}{2}(A_1+A_2)$
We have $ \sum_{i=1}^{15}b_i-\sum_{i=1}^{15}a_i=\dfrac{15}{2}[b_1+b_1(15-1)d_2)-(a_1+a_1+(15-1)d_1)$
$=7[3+73-1-55]$
$\sum_{i=1}^{15}b_i-\sum_{i=1}^{15}a_i=975$
