I am currently solving some Standardized test questions involving ratio rates.

I managed to solve cross multiplication word problems involving two columns which ended with something like

3 : 5

4 : x

so we get something like 3x = 20

I remember i also was (good) in solving problems with more than two columns something like

Men days Work

6 10 1/3

4 x 2/3

Which ended with equations like

6x10x2/3= 4x X x (1/3)

The above is just a part of an example. Does anyone know how you solve problems like the ones above with more than 2 columns ? Any suggested reading material that highlights the above trick ? What is this trick called ??