terrarium fund

there is $5 in my terrarium fund
i will clean for 15 minutes and pledge $5 more to the fund
new total: $10
now i will clean for 15 more minutes. i pledge $5 more to the fund
new total: $15
now i will work for 20 minutes. i pledge $5 more to my fund.
new total: $20
now i will clean for 20 minutes. i pledge $5 more to my fund.
new total: $25
now i will clean for 20 minutes. i pledge $5 more to my fund.
new total: $30