Answer:
10,
Step-by-step explanation:
The bottom right angle is 45 degrees so the top left must also be 45 degrees (180 - 45 - 90 = 45). This means that x is the same as the left side: 10.
The triangle is right angled so we can use pythagoras on it: x^2 + 10^2 = y^2 = 200
y = √200 = √100√2=10√2
