My strategy to solve this problem

26+?=70

                                / \    /\

                 20+6+4=30 30+40=70

I will expand the 26 into  a 20+6.  The 6 ones will need 4 ones to make ten. 6+4=10.
So 20 + 10 makes 30.  

30 needs 40 more to get to 70. The answer will be 4+40=44

26+44=70

Today I was learning how to solve a problem. It was really easy.