By the looks of it the hieght is 7 and base is 6 so
A= 1/2(6)(7)
A= 1/2(42)
A= 21
4.15, 6.3, 8.45, 10.6, 12.75
You just subtract 4.15 from 6.3 and you get a difference of 2.15. Then you add it to 8.45 giving you the answer of 10.6 and then you add 2.15 to that getting 12.75.
The original expression is given by:

The correct way to rewrite the expression is given by:

For this, we use two properties:
Associative property:
The way of grouping the factors does not change the result of the multiplication:
Commutative property:
The order of the factors does not vary the product: