X/15+1/3+115 = x/12 gives x=24.

3. let the middle number be x.

X-7+X+X+7=42 gives X= 14, x-7=7, and the smallest number is 7.

4. Suppose that X people are arranged to work first. According to the meaning of the question

4 * x/40+2 *1/40 * 8+8 * x/40 =1gives x=2.