To find the area you need to look at the triangle and the square as two seperate areas then add the together.
First
You would divide the 5 meters up so 1 meter is the base of the triangle and 4 meters goes to the lenght of the square.
Second
The formula for the are of a triangle is
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b being the base and h being the height. When you input the numbers itll be

when you multiply 1, 4, and half you get 2m²
Third
For the square simply mutiply base tims height or in this case 4x4. which will give you 16m²
Last
you add 16 and 2 for you answer of 18m²