To solve this question, we should convert the information we have to a system of equation.
Let x=speed of Carl's painting, in jobs/hour
Let y=speed of Jen's painting, in jobs/hour
We know from the first sentence:
x=3y
Together, they can complete a whole job in 2 hours, which means they complete half a job in 1 hour when they work together
Therefore:
x+y=1/2, meaning Jenn and Carl working together completes half a job/hour
We can substitute 3y for x in this equation to find Jen's rate:
3y + y = 1/2
4y=1/2 Divide both sides by 4
y=1/8
Jenn completes 1/8 of the job in 1 hour, so it would take her 8 hours to do the job herself.