Me! i've tried so hard and just cant

So... 4 folks, working for 8hours per day, do it in 15days

hmm alrite...so 4 folks working for 8hrs in 1 day, each one does 8, 4 of them, 4*8 = 32, so, they do 32 workhours every day, now for 15 days, that'd be 32*15, or 480

so, the whole job really takes 480 hours

now hmm let's see, the firm decides to increase the folks, but decrease the hours, so, 5 folks each working 6hours every day

how many workhours total? well 5*6 = 30
each is working 6hrs, 5 of them, so 30 workhours

how long will it take them if they only do 30 workhours everyday?

well the whole job is 480hours