PR is 10.
Sine is the ratio of the side opposite an angle to the hypotenuse. 0.8 is read as "eight tenths," so this would be 8/10. We generally denote a right triangle using the letter of the right angle in the middle, so we will assume that Q is the right angle. This means that PR is the hypotenuse. Since sine = opposite/hypotenuse, sine = 8/10 means that the hypotenuse is 10.
