Question 898438
How you solve it depends on what you have learned so far.
Do you know the  relationship of sides in isosceles right triangles 45-45-90?
Are two sides equal?
Do you know the  relationship of sides in 30-60-90 right  triangles?
Is one side 2x another side?
Can a triangle with sides 40,50,80 have a 90 degree angle?
Use Pythagorean formula.