Bryce wrote the linear regression equation y=1.123x-6.443 to predict the armspan, y, of a person who is x inches tall. riley has an armspan of 67.5 inches. which is the best prediction of riley’s height? a ) 54.36 inches b ) 65.84 inches c ) 66.55 inches d ) 69.36 inches

For this case what you should do is use the linear equation that Bryce wrote and replace the corresponding value of y which is 67.5 inches. Then, you must clear x to find the height.
 We have
 y = 1.123x-6.443
 67.5 = 1.123x-6.443
 Clearing x
 x = (67.5 + 6.443) / (1.123) = 65.84
 The best prediction of Riley's height is 65.84 inches.
 answer
 B) 65.84 inches

Could you make it more clear?