I need help quick please help 1/y = 4/21

Which statement is true 1.the pythagorean theorem can be used to find the missing side of any triangle 2.the pythagorean theorem can be used to find the missing side of any polygon 3. the pythagorean theorem can be used to find the missing side of any right triangle 4.the pythagorean theorem can be used to find the missing side of any isosceles triangle

Someone me! if you’re smart you can solve this!

To decrease an amount by 16% what single multiplier would you use