I think the assessment you need to make in this question is: What will happen if someone joins their efforts to finish something. Based off the information given, the answer would be C - 24 Minutes. Why? Well let's think about it a bit.
We will put this into a math problem using the variable c for Colleen and s for Sanford:
Sanford can only build 1 computer in 60 minutes:
1 = s*60
Solve for s: s= 1/60
Colleen can only build 1 computer in 40 minutes:
1 = c*40
Solve for c: c= 1/40
Now we need to figure out how much time it would be for both to build a computer together, t is a placeholder for time:
1 = (s + c) * t or [tex]t=1/(s+c)[/tex]
Plug in your values:
[tex]t= \frac{1}{(\frac{1}{60}+\frac{1}{40})} = 24 Minutes
[/tex]
