Answer: $25.90
Explanation:
We will have x as the youngest son's share, (the youngests son's share is the basis)
(x + 4.30) as the eldest son's share, (the eldest received 4.30 more than the youngest)
(x - 7.80) as the second son's share, (the second received 7.80 less than the youngest)
and 64.90 as their share altogether.
To find the youngest son's share:
(x) + (x + 4.30) + (x - 7.80) = 64.90
x + x + 4.30 + x - 7.80 = 64.90
x + x + x = 64.90 - 4.30 + 7.80 (group all of the like terms together. variables with variables, numbers with numbers. 4.30 became negative since it was moved to the other side, the same happened with 7.80 since it was a negative, it became a positive when it moved to another side)
Solve...
x + x + x = 64.90 - 4.30 + 7.80
3x = 68.40 (divide both sides by 3)
x = 22.80
(The youngest son's share is $22.80)
To get the eldest son's share:
x + 4.30 (substitute x since it has already been solved)
22.80 + 4.30 = 27.10
The eldest son's share is $27.10