let the digits of the two digit number be

x on the one'e place

y on the tent's place

then we can write the number is 10y + x

the sum of the digits of the number is 9

x + y = 9

the number is 12 times the tens digit

10y + x = 12y

by solving the system of equations

x + y = 9

10y + x = 12y

we find

x = 6

y = 3

the number is 36.