Hello there, I hope you are doing mighty well.
The answer is going to be 8.75 m.
In order to find the area of (almost) any shape is to multiply the shapes' width by its height.
As opposed to this diagram, the width of the garage is 3.5. The height is either mainly on the left or right side of a shape going from down to up or up to down, but all that matters is the value (or, the value (number) as opposed to the height). The height is 2.5, as displayed in the diagram.
So, we take the width of 3.5 and multiply it by the length of the height, which is 2.5.
3.5 * 2.5 = 8.75
You get the sum (or solution in some cases) as of 8.75.
I hope this helped; I tried my best to explain it well as I was able to.