Rectangle ABCD

1) Figure out 3 other side values from the given 18cm. 

So, all sides added together equal to 56cm. In a rectangle the opposite sides must be the same. So if one side is 18cm, the opposite side will also be 18cm. Then add the two together and minus it from the total. 

18+18 = 36

> 56-36 = 20cm

If you have 20 as rhe answer, all you have to do is divide by two, because you have two remaining sides to find. 

20/2 = 10

So the length values are: 18 and 18

and the width values are 10 and 10

2) Make sure you write down the information already given to you. 

E.g. Total perimeter, triangle areas etc. 

3) The area of the triangle inside ABF is already given to you. This is what we'll use to figure out BEF.

To find BEF we first need to find ABE. 

A= (bxh)/2

A= (18x10)/2

A= 180/2

A= 90cm

4) Taking away 42cm from the total 90cm will give us the area of triangle BEF

90-42= 48

Therefore, triangle BEF= 48cm