Question 447072
1/x+1/(x+8)=1/3
3x+24+3x=x2+8x
x2+2x-24=0
(x+6)(x-4)=0
x=-6 or 4
Throwing out the negative answer, we get the larger unit needing 4 hours to melt the iron, and the smaller unit needing 12 hours..