Yesterday, stanley's doughnut shop sold 2/3 as many chocolate doughnuts as cinnamon doughnuts. if they sold 7 1/4 trays of cinnamon doughnuts, how many trays of chocolate doughnuts did they sell?

You figure out the amount of chocolate doughnuts sold by multiplying 2/3 by 7 1/4

first you change 7 1/4 to an improper fraction:
7 1/4= 29/4
now multiply 2/3×29/4 by multiplying the two numerators then putting that over the two denominators multiplied: (2×29)/(3×4)=58/12
now simplify:58/12=4 10/12= 4 5/6

the answer is Stanley's doughnut shop sold
4 5/6 trays of chocolate doughnuts