Rodney can build a cabinet alone in 16 hours:
This means that Rodney builds 1/16 of a cabinet per hour
Together they build 1 cabinet in 12 hours. If we call the
time it would take Tomaso to build a cabinet alone T, then
Tomaso does 1/T parts of a cabinet per hour
The sum of (1/16 + 1/T) is thus finished each hour.
This must sum to 1/12 since it takes 12 hours together to build a cabinet.
1/16 + 1/T = 1/12
Multiply through by Lowest Common Multiple of 12 and 16 ... 48
3 + 48/T = 4
48/T = 1
T = 48
Tomaso would take 48 hours to build a cabinet alone.