Respuesta :
Given that on day 15 the balance was $0 and on day 16 the balance is $100, then we have:
[tex]\begin{gathered} \text{slope:} \\ m=\frac{y_2-y_1}{x_2-x_1} \\ \Rightarrow m=\frac{100-0}{16-15}=100 \\ \text{for point (15,0) and slope m=100:} \\ y-y_0=m(x-x_0) \\ \Rightarrow y-0=100(x-15) \\ \Rightarrow y=100x-1500 \end{gathered}[/tex]we have that the relation function for this period is B(x)=100x-1500. Then for x=21 we have the following:
[tex]\begin{gathered} B(x)=100x-1500 \\ B(21)=100\cdot21-1500=2100-1500=600 \\ \end{gathered}[/tex]therefore, using the relation function, we have that B(21) = 600.
To find the amount of money deposited into the account after day 16, we have to find B(17), B(18), B(19) and B(20):
[tex]\begin{gathered} B(17)=100\cdot17-1500=1700-1200=200 \\ B(18)=100\cdot18-1500=1800-1500=300 \\ B(19)=100\cdot19-1500=1900-1500=400 \\ B(20)=100\cdot20-1500=2000-1500=500 \end{gathered}[/tex]