y=40+5x
For an example, say Mia wanted to add $5 into her account each week for 2 weeks.
y=40+5(2)
5(2)=10
y=40+10
y=50
Mia will have a total of $50 in her account if she added $5 for each week for 2 weeks. Same for Juan, his equation will be based off his amount y=15+10x