Let P$=0\mathrm{.}001$ BTC and Q$=0\mathrm{.}002$ BTC$,$ first $2$ years compounds at $4$P per month for $24$ terms with monthly deposits. $3$ and $4$ years compounds $4$Q monthly for $24$ months till the end of year $4$ while also compounding the previous $2$ year $4$P deposits. I got the first sigma notation to be top index$=24,$ bottom index: k$=1,$ term is $4$P$(1+$r$/12)^$K$,$ but have trouble figuring out what steps to take for the second sigma notation i know one of the terms will be $4$Q$(1+$r$/12)^$K like the first one but how should i go about showing that the previous $2$ year deposits are being compounded but not being deposited going forward.