Worksheet.function question

Hello,

My question:

When using the worksheet.function method in VBA, what code would one use to copy the result to all applicable cells in each applicable rows. My code is below:

Range("M3") = WorksheetFunction.Sum(Range("K3:L3"))

I need the above result for M4, M5, M6, etc. and I don't want to right the above code multiple times for each row of data. Thanks.