Hope this helps.
If not, go to: https://www.mathportal.org/calculators/financial-calculators/simple-interest-calculator.php
From the Special Triangle Theorem, the hypotenuse is equal to the side lengtht times the Sqrt(2).
So hypotenuse H = xSqrt(2), x=H/Sqrt(2).
Using numbers, if H = 7, then x = 7/Sqrt(2) = 7Sqrt(2)/2 to rationalize it.
The answer is X=4.
It is both parallel to x=-3 and passes through (4,2)