#a
Use geometric progression formula
Here
First term =2(20)=40
Equation
[tex]\\ \rm\Rrightarrow y=40(2)^{n-1}[/tex]
After a year
[tex]\\ \rm\Rrightarrow y=40(2)^{11}[/tex]
[tex]\\ \rm\Rrightarrow y=40(2048)[/tex]
[tex]\\ \rm\Rrightarrow y=\$81920[/tex]
#b
It's arithmetic as common difference is 50
[tex]\\ \rm\Rrightarrow a_n=a+(n-1)d[/tex]
Equation
[tex]\\ \rm\Rrightarrow a_n=80+(n-1)50[/tex]
After a year
[tex]\\ \rm\Rrightarrow a_{12}=80+11(50)[/tex]
[tex]\\ \rm\Rrightarrow 80+550[/tex]
[tex]\\ \rm\Rrightarrow \$630[/tex]