Answer:
(D) $780 in 2015.
Step-by-step explanation:
The computation is shown below:
For 2014
The gross income = Per month cost × number of months + Per month cost × number of months
= $40 × 6 months + $30 × 6 months
= $240 + $180
= $420
For 2015
The gross income = One year cost - (Per month cost × number of months) + two year cost - (Per month cost × number of months)
= $480 - ($40 × 6 months) + $720 - ($30 × 6 months)
= $240 + $540
= $780
The 6 months is calculated from July 1 to December 31