I don't know what they mean by dimensions ?

Always remember to start by writing down what you know for sure from what they tell you in the problem. The first piece of information is that the figure is a rectangle, and the second is that they are giving you the area. So, start with the formula for the area of a rectangle, Area= (B) * (H). Now put in the rest of the information they've given you. This Area is equal to 27 square ft. So substitute 27 for A in the equation above. 27 = B*H.

Now, as Sheila recommended, describe the relationship between the base and height in numbers:

B=2H +3 ("The base is equal to 3 more than (use addition) twice (multiply it by two) the height."

Now you have quantities that describe the relationship between base and height (the Area) and a quantity for one in terms of the other. Can you put these together? Sure you can! Put the description for B in the Area formula.

27 = H(2H +3) ... If you distribute the H through the parentheses and bring the 27 over to the right hand side of the equation..... you'll be headed toward a trinomial that needs factoring. You'll actually get two answers, but one of them doesn't fit the requirements of the question, so you can throw it out.... Always remember to check your answer to see if it fits.

Now that you have dimensions that fit the area requirement, you can label your rectangle and add up the side lengths to get the perimeter.

Good luck.