You have provided insufficient information.
Here is one approach:
Make a sketch of the property and label all five sides with the info you just gave us.
Next, draw two diagonals from one of the corners to two opposing corners such that you have divided your figure into three triangles.
Measure the lengths of the diagonals and add them to your drawing. Now you have sufficient information to calculate area using Heron's Formula:
http://www.mathsisfun.com/geometry/herons-formula.html
Calculate the three triangle areas and add them up. If your length measurements were in feet, your answer will be in "square feet" or "feet squared." You can use the Internet to get a conversion into acres.
Hope that helps.