Each "contour" is a pair of parallel lines with slope 8.
Answer:
$121.51
Step-by-step explanation:
At 18.7%, the monthly multiplier is 1+.187/12, so for the year, James' balance is multiplied by (1+.187/12)^12 ≈ 1.2038899
At 12.5%, the monthly multiplier is 1+.125/12, so for the year, James' balance is multiplied by (1+.125/12)^12 ≈ 1.1324161
The difference in these multipliers is ...
1.2038899 -1.13241605 = 0.0714739
so James' savings is ...
$1700 × 0.0714739 ≈ $121.51
