How about trying to make 90 using the digits 1-8 and leaving the 9 for adding 
on at the end?<br>
A good place to start may be to push the 1 and 2 together to make 12. What will 
you still need to add onto 12 to make 90? Can you make 90 simply by adding the 
remaining digits together? What could you do?<br>
Perhaps you could try pushing the 2 and 3 together to make 23? What do you need 
this time to make 90?