Answer:
x = 6 km
Step-by-step explanation:
Let x be distance in km
The inequaqlity is
5 + 2.5*x ≤ 20 (1)
And the maximum distance will be when the inequality (1) get the upper limit that means when (1) becomes an equality
5 + 2.5x = 20
2.5 x = 15
x = 15/2.5
x = 6 km