Hey there :)
We need to use trigonometry here
Given is the angle = 30°
And one side = 26
With a missing side = x
The missing side is the opposite of the given angle, we have the adjacent but we don't know the value of the hypotenuse, so we need to use Tangent
Tan α = [tex] \frac{opposite}{adjacent} [/tex]
tan 30 = [tex] \frac{x}{26} [/tex]
26tan(30) = x
x = 15