Because the triangle is isosceles, we know that it has 2 equal sides, which are the 2 legs. We can create an equation with the given information:
26 = 2(b + 4) + b
26 = 3b + 8
18 = 3b
b = 6
If the base is 6, add 4 to get 10.
base = 6 meters
leg = 10 meters
other leg = 10 meters
Hope this helps! :)