To start this is a ratio, and the goal is to get at least 1 to be a whole number so first lets get the number below 1 to 1.
0.75 : 2 5/16 ---> (x1.3333 on both sides) ---> 1 : 3 1/12.
Next, if needed for your answer, lets get the other number to be a whole number as well. We can do this my multiplying both sides by 12 since the fraction on 3 1/12 is 1/12.
1 : 3 1/12 --> (x12 on both sides) ---> 12 : 37
Your final answer will either be 1 : 3 1/12 or 12 : 37, depending on the formatting expected for your homework assignment.