To solve this you must use Pythagorean theorem:
![a^(2) +b^(2) =c^(2)](https://img.qammunity.org/2020/formulas/mathematics/college/ysyqcuv7zowodz5o2fvprirk5nq313c0wc.png)
a and b are the legs (the sides that form a perpendicular/right angle)
c is the hypotenuse (the side opposite the right angle)
In this case...
a = 5
b = 8
c = x
^^^Plug these numbers into the theorem
simplify
25 + 64 =
![x^(2)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ep4nmi8emgex7xa4trp0z22cf0a8lzzrpe.png)
89 =
![x^(2)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ep4nmi8emgex7xa4trp0z22cf0a8lzzrpe.png)
To remove the square from x take the square root of both sides to get you...
√89 = x
(choice A)
Hope this helped!
~Just a girl in love with Shawn Mendes