1/7 of Matthew's allowance is equal to 3/8 of Ryan's allowance. What is the ratio of Matthew's allowance to Ryan's?

let Matthew's allowance be m

let Ryan's allowance be r

"1/7 of Matthew's allowance is equal to 3/8 of Ryan's allowance"
(1/7)m = (3/8)r
8m = 21r
m/r = 21/8

m : r = 21 : 8