Answer: it will take the faster computer 15 minutes to do the job on its own.
Explanation:
Let t represent the number of minutes it will take the faster computer to do the job on its own. It means that the rate at which it does the job per minute is 1/t
If it takes the slower computer 30 minutes to do the job on its own. It means that the rate at which it does the job on its own per minute is 1/30
By working together, they would work simultaneously and their individual rates are additive. Working together it takes two computers 10 minutes to send out a company's email. It means that the rate at which both computers work together per minute is 1/10 Therefore,
1/t + 1/30 = 1/10
Cross multiplying by 30x, it becomes
3x = x + 30
3x - x = 30
2x = 30
x = 30/2
x = 15 minutes