State if each pair of ratios forms a proportion. 4/2 and 20/6. some one explain

For two numbers to be in proportion, the products obtained when we cross multiply them. When the numerator of the first ratio is multiplied to the denominator of the second, the product should be equal that when the numerator of the second is multiplied to the denominator of the first.
                       4 x 6 = 24   and  2 x 20 = 40
Therefore, the pair is not proportion. 

It would be the second one because it passes the vertical line test