To solve this you must use Pythagorean theorem:
a and b are the legs (the sides that form a perpendicular/right angle)
c is the hypotenuse (the side opposite the right angle)
In this case...
a = 48
b = x
c = 50
^^^Plug these numbers into the theorem
simplify
2304 +
= 2500
Isolate x^2 by subtracting 2304 to both sides
= 196
To remove the square from x take the square root of both sides to get you...
14 = x
Hope this helped!
~Just a girl in love with Shawn Mendes