start by finding the measurement missing using the pythagorean theorem
![\begin{gathered} 30^2-12^2=x^2 \\ 756=x^2 \\ x=\sqrt[2]{756} \\ x\cong27.5 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/ota09jg8de6d99oy2fxu02rttou0z85zzk.png)
add all measurement together to find the perimeter of the backyard
![27.5+30+12=69.5](https://img.qammunity.org/2023/formulas/mathematics/college/isccbm8npumt68yimqlnszy1v9thwxllvp.png)
if the bushes are wanted 3 feet appart from each other divide the perimeter by 3
![(69.5)/(3)\cong23](https://img.qammunity.org/2023/formulas/mathematics/college/q3wqmbv9auainshi26wavowgscihwgkt4n.png)
Mrs. Cheung's backyard is going to need 23 bushes