For this case, the first thing we must do is define variables. We have then: x: number of years of Joan y: number of years of ellen We now write the system of equations: [tex] y = x + 5
(x-3) + (y-3) = 17[/tex] Solving the system we have: [tex] x = 9
y = 14[/tex] So that Joan is 21 years old then: [tex] j + 9 = 21
j = 21 - 9
j = 12[/tex] Answer: joan will be 21 years old in 12 years
