Janice and her brother James want to raise money to go to band camp. Their parents have agreed to help them earn up to $300 by paying them $21 when one of them mows the lawn and $10 for each hour that one of them babysits their younger brother. They will have to do a combination of both chores in order to earn the money. Select the equation that represents the number of lawns they can mow, m, and hours they can babysit, b, to earn $400. (4 pts.)

a
\large 25m-10b=400

b
\large 300m+10b=21

c
\large 21b+10m=300

d
\large 21m+10b=300