Question

2.) If the aspect ratio in width to height (width: height) of a chalkboard is 16:9 and

Answer 1

Essentially we must find a height such that 70:height is at the same ratio as 16:9. So

16/9=70/h
1.778=70/h
1.778h=70
h=70/1.778=39.37inches

Check work:
16:9 = 1.7777778
70:39.37 = 1.778