The trick here is to realize that 

"2 consecutive multiples of 3"

means 

"2 consecutive integers, each multiplied by 3"

Let the first consecutive integer be n
Then the second consecutive integer is n+1

So,

the first consecutive multiple of 3 is 3n 
the second consecutive multiple of 3 is 3(n+1)

So,

3n + 3(n+1) = 69

Solve that and get the the two consecutive integers,
then get the two consecutive multiples of 3.

Edwin