Ok. We have this for input:
Al: 7 logs + 4 dogs
Cal: 3 logs + 11 dogs
Del: $15
There are 4 + 11 = 15 dogs. Split evenly that's 5 dogs per person
There are 7 + 3 = 10 logs. Split evenly that's 10/3 logs per person
We know Del's $15 contribution was considered fair.
Let L = value of a log, D = value of a dog
Del's equation is: 10/3 L + 5 D = $15
If the 10 logs are worth 4 times the 15 dogs, we have 10L = (4 * 15) D, giving us L in terms of D:
10 L = 60 D ; L = 6D
Back to Del's equation, and substitute 6D for L:
10/3 (6D) + 5D = $15
20D + 5D= $15
25D = $15
D = 15/25 = $0.60 Now we have the value of a dog!
Back to Del's equation, use the value of a dog in place of D, and figure out what L is:
10/3 L + 5 ($0.60) = $15
10/3 L + $3 = $15
10/3 L = $12
10 L = $36
L = $36/10 or $3.60
Dogs are worth $0.60 and logs are worth $3.60.
Figure out the value of the items brought by Al and Cal:
Al = 7 * 3.60 + 4*0.60 = 25.20 + 2.40 = $27.60
Cal = 3*3.60 + 11*0.60 = 10.80 + 6.60 = $17.40.
17.40 + 27.60 = $45... so $15 is indeed each boy's share. Subtract the per-person share from the total value each boy brought and you have the amount of Del's $15 each boy receives:
27.60 - 15 = $12.60 for Al
17.40 - 15 = $2.40 for Cal
Voila!