Answer:
It will take Jack about 7.1 hours alone
Explanation:
You are given the equation
t/a + t/b = 1
where t is the time working together, a is the time Jill spends working alone, b is the time Jack spends working alone
Substituting these numbers in
3.2/5.8 + 3.2 /b = 1
Multiply both side by 5.8b to clear the fractions
5.8 b * (3.2/5.8 + 3.2 /b )= 1*5.8b
Distribute
3.2b + 5.8*3.2 = 5.8b
Subtract 3.2b on each side
3.2b -3.2b+ 5.8*3.2 = 5.8b-3.2b
5.8*3.2 = 2.6b
18.56 = 2.6b
Divide by 2.6 on each side
18.56 /2.6 = 2.6 b/2.6
7.138 = b
It will take Jack about 7.1 hours alone