Millie has box which contains 100 cubes
She has a bag which contain 70 cubes
so total cubes she has is 170 cubes
If she is making a train of 10 cubes so,
170 / 10 ( because one train has 10 cubes)
= 17 trains out of 170 cubes.
Ans = 17 trains
:) hope I helped you