Use Pythagorean theorem.
[tex]x^2+4^2=5^2\\\\x^2+16=25\qquad\text{subtract 16 from both sides}\\\\x^2=9\to x=\sqrt9\to x=3\ (cm)\\\\y^2+4^2=7.5^2\\\\y^2+16=56.25\qquad\text{subtract 16 from both sides}\\\\y^2=40.25\to y=\sqrt{40.25}\\\\y\approx6.34\\\\x+y=3+6.34=9.34\approx9\ cm[/tex]
Answer: B. 9 cm.
