Christine used 12 cubes to make this 3-step staircase. if she used a total of 56 cubes to make a similar staircase, how many steps will the staircase have?

a.) 6 steps
b.) 7 steps
c.) 8 steps
d.) 9 steps

What we have here are steps where each step requires twice as many blocks as the height of the steps. If you would like to check this math we can look at the staircase given:
3x2 + 2x2 + 1x2 = 6 + 4 + 2 = 12. 

We can see that the math works, so now we can do the same work to find out how many steps 56 cubes can make. 

6x2 + 5x2 + 4x2 + 3x2 + 2x2 + 1x2 = 42 (6 steps)
7x2 + 6x2 + 5x2 + 4x2 + 3x2 + 2x2 + 1x2 = 56 (7 steps)

Therefore, the answer is B. 7 steps.