This one you can't really make a formula for or anything, but it's fairly simple to figure out, with a bit of guess and check.
14 is really close to 15, but that's bigger, so let's try a smaller number that would work.
It has to be divisible by 2, because you've got a whole number that is 3 1/2 times the other number. (1/2 of a whole number means it's divisible by 2).
10 is divisible by 2,
10 ÷ 2 = 5
But, 10 x 3 = 30 which is much bigger than 14.
So, we've got to start with a smaller number.
Let's try something really small, like 4. We could try 2, but 2 x 3 = 6, which, even with 1/2 of 2, isn't nearly close to 14.
Now, 4 x 3 = 12
That's quite close to 14.
And 1/2 of 4 is 2.
All we do now is add 12 to 2 and see if it works.
12 + 2 = 14
14 = 14
This one works.
That means that Gina volunteered for 4 hours, because 3 1/2 x 4 = 14.
