Answer

12 kilometers per hour 🎯

Solution

The problem is under systems of linear equations in algebra.

Let r = running speed on flat ground
Let h = speed change on inclined road

Equation 1: r + h = 15
Equation 2: r - h = 9

To get the value of r, just add Equation 1 and Equation 2.

2r = 24
r = 12

Therefore, @jancharlest's running speed on even ground is 12 kilometers per hour. It can't get easier than that. 😆

Winner: @jfang003 🏅

1 HIVE has been sent to @jfang003's Hive account. 💰

Mentions: @holovision, @eturnerx (@eturnerx-dbuzz) and @ahmadmanga (@ahmadmangazap)
Special mention: @chrisrice