Five less than twice a number is equal to 57

The easiest way to do this is to break it down and translate it before solving. Start with twice a number, if you use n to represent eh number, you will have 2n. Then, add the 'less than' part. 'Five less than' means that five is being subtracted from the next part, which is 2n. Now you have 2n - 5. The last translation is simple, 'equal to 57' will complete the equation as 2n - 5 = 57.
If you want to solve the equation, use the Order of Operations.

2n - 5 = 57    Add 5 to both sides
     2n = 62    Divide both sides by 2
       n = 31