Initial investment = $100
The balance increases annually at a rate = 4%
The increased amount = 4% of $100
This gives
[tex]\frac{4}{100}\times\text{\$}100=\text{\$}4[/tex]Hence the investment increase annually by $4 yearly
In the second year the investment will increase by 2 x $4 = $8
In the third year the investment will increase by 3 x $4 = $12
This implies that
In n years
The investment will increase by n × $4 = $4n
The balance at n years is given as
Balance = Investment + year increment
This is as shown below
[tex]\text{Balnace }=\text{ \$100 }+\text{ \$4n}[/tex]