How would you get the equation to figure the area out?

1.(Rectangle) the length is 3x - 2 and the width is 4.





2.(Triangle) the height is 5a + 7 and the base is 18.





3. (Triangle) the height is 13 and the base is 6 - 2y





can you give me the equation to figure out the area. I looked in the back of the book to get the idea but, I also have to know how I got it. I already know the answer to the second one. It's (45a + 63) units 虏How would you get the equation to figure the area out?
For a rectangle, it is length * width.


For a triangle, it is 1/2 base * height.How would you get the equation to figure the area out?
1. area = length x width = 4(3x-2)





2. area = (1/2)base x height = (1/2)18(5a+7)





3. area = (1/2)13(6-2y)