Are 6/10 and 6/30 multiples of 3/10 ? explain

6/30 and 6/10 are not multiples of 3/10 because you cant take 3/10 and multiply both the numerator and the denominator by one number and get 6/30 or 6/10 but a multiple would be like 6/20, 18/40, 30/100 and so on.   

Use pythagorean’s theorem and find the missing side lengths of the two smaller triangles and add them together
13^2 - 12^2 = 5
15^2 - 12^2 = 9
5+9 = 14
14 is the length of each side of the square
14^2 + 14^2 = 19.8
19.8 is the diagonal length of the inside if the square

Just use long division to write it out