let

c = the number of crayons

m = the number of markers

There are 9 more markers than crayons:

m = c + 9

There are 17 items in all:

m + c = 17

plug m = c + 9 into the last equation

c + 9 + c = 17

by solving we find:

c = 4

m = 4 + 9 = 13

the two numbers are 4 and 13.