A= 1.142 m/hr
Width of beach at 8 p.m. = 36 m
Width of beach at 3 a.m. = (36-8) m =28 m
Average change in width(A) = change in width (Width of beach at 8 p.m.-Width of beach at 3 a.m.0/ time in hours
A= ( 36-28)/ 7
A= 8/7 m/hr
A = 1.142 m /hr
Hold on let me solve this problem meet em in the comments for the awnser