Sum range of numbers based on Name and Month

Please help...
I'm trying to sum numbers in a column based on a range of Months & Names. I recently received a formula that counts the number of times a name appears in a month works great: =SUMPRODUCT(--($K$17:$K$29=$S20),--(TEXT($M$17:$M$29,"mmmyyyy")=TEXT(T$19,"mmmyyyy")))
I'm trying to sum total hr's so I can see how many jobs an employee takes and the time it took to complete that number of jobs per month. I've tried to use the above code sent to me by one of your members by revising it by adding count, countif, etc. so many different tries. The closest I gotten was summing up all of the same names or I get "=name" or "0".

Data sample:
rng1...rng2...rng3
a..........b........c
joe2 2 23-Feb
joe1 3.5 16-Apr Joe1 month of Apr = 6 (day doesn't matter)
joe1 2.5 16-Apr
joe1 3 2-May Joe2 month of Feb = 2 (day doesn't matter)
joe3 2 27-Oct Joe3 month of oct = 2 (day doesn't matter)

If you can help please explain how the formula works.