Answer:
4,646.30
Step-by-step explanation:
The sum of n terms of geometric sequence can be calculated using formula
[tex]S_n=\dfrac{a_1(1-r^n)}{1-r}[/tex]
In your case,
[tex]S_n=86,830\\ \\r=2.2\\ \\n=4\\ \\a_1=?[/tex]
Substitute into the formula:
[tex]S_4=\dfrac{a_1(1-2.2^4)}{1-2.2}\\ \\86,830=\dfrac{a_1(1-23.4256)}{-1.2}\\ \\-104,196=a_1(-22.4256)\\ \\22.4256a_1=104,196\\ \\a_1=\dfrac{104,196}{22.4256}\approx 4,646.30[/tex]
