Answer:
6
Step-by-step explanation:
[tex]\triangle{PQR}[/tex] is a right triangle. Use the Pythagorean Theorem:
(leg)^2 + (leg)^2 = (hypotenuse)^2
The length of PR is r + 4; it's the hypotenuse.
[tex]PQ^2+QR^2=PR^2[/tex]
[tex]r^2+8^2=(r+4)^2 \\ r^2+64=r^2+8r+16 \\ 64=8r+16 \\ 48=8r \\ 6=r[/tex]
Remember, to expand [tex](r+4)^2[/tex] you multiply [tex](r+4)(r+4)[/tex]
