First we need to find the length of the missing triangle side which we can do with Pythagorean theorem
A2+B2=C2
5^2+3^2= x^2
25+9=x^2
34=x^2
You square booth sides and end up with a decimal of 5.831 rounded for the missing side.
Area for a rectangle is length times width so we multiply 7x5.831=40.817
Area of a triangle is the height times the base divided by 2 so 5.831x3= 17.493
Then you add those to together for the total area of the shape 40.817+17.493=58.31
58.31 is your approximate answer.