Acalculator has 50 keys in five colors: gray, black, blue, yellow, and green. there are 6 gray keys for every 7 blue keys. write the possible ratios for gray to blue keys

A ratio is written in the form a : b. In this case, there are 6 gray keys for every 7 blue keys. So the ratio for gray to blue keys would be 6:7. 
Since 6 and 7 don't have common factors, the ratio 6:7 cannot be simplified further. 
So the ratio for gray to blue keys is 6:7.