The estimate, 4 × 5 = 20, helps me
know that the decimal point should be placed so that the answer is close to 20.
Here another way to check using system of linear equations. there are two ways of doing this either by substitution or elimination but I chose to do elimination because it’s a bit easier.
The area of this figure is 532m.
First you do the square which is 18 time 18 gets you 324m.
The for the first triangle you would do 18 times 16 then divide by 2 which is 144m.
For the last triangle you would do 16•8 div by 2 which will give you 64m.
Add them all up and you get 532m.
The first one is 14.6. The second is 17.8