Question

https://photos.app.goo.gl/Sp5b6Td3uLgjn3q49

Answer 1

Let h = the height of all the boards = ?
Let x = the number of boards =9
Let t = the thickness of each board = 3*2/3 cm = 0.78 inches
We know that the number of boards * the thickness of each board = the total height.
So we can express this in an equation as follows:

x * t = h

We know t and x, so enter them in:
9*0.78= 7.02 inch
height = 7.02 inch
height =17.83 cm