Set up the problem as follows:

R = the number of hours Ron Worked

number of hours Mary worked = (2R +3)  (2R is twice the amount of hours that Ron worked, and add 3 to get 3 more hours, as stated in the problem.)

They worked together a total amount of 57 hours, so an equation can be written as follows:

R + (2R +3) = 57.

Then, solve for R.

First combine like terms to make:  3R + 3 = 57.

Then, subtract 3 from both sides to leave 3R alone on the left side.

3R = 54.

Finally, divide both sides of the equation by 3 to get R.

R = 18.

Therefore, Ron worked 18 hours, and Mary worked:

(2R + 3) = 2 (18) + 3 = 39 hours Mary worked.

Do a quick double check to make sure this makes sense.

Ron's hours + Mary's hours = 57 hours.

18 + 39 = 57.  We are correct.

Let's assume that Ron worked "h" hours, then Rhonda worked (2h + 3) hours, together they worked 57 hours.
h + 2h + 3 = 57 ---> 3h = 57 - 3 ---> 3h = 54 ---> h = 18 , Ron worked 18 hours.
18 × 2 + 3 = 39 , Rhonda worked 39 hours.