40 leads a month, and 30% of them slip through without follow-up. That is 12 leads.
At a 25% close rate on leads that are followed up, those slipped leads would have been 3 jobs.
At $1,500 a job, that is $4,500 a month, or $54,000 a year.
Recovering 50% of the slipped leads is 1.5 jobs, or $2,250 a month ($27,000 a year).
Slipped leads are counted as if they would close at the same rate as leads that get follow-up.