: H = Heather's age
R = Rachel's age
first sentence: H = R/2 + 3
second: |H - R| ≤ 4
Sub for H: |R/2 + 3 - R| = |3 - R/2| ≤ 4
At the endpoints we have
3 - R/2 = 4 which doesn't have a positive solution
3 - R/2 = -4 → R/2 = 7 → R = 14
Check: H = (14/2) + 3 = 10 √
Rachel must be an even number of years old (we divide her age by 2).