Let’s first cut/separate this figure into two shapes: rectangle and a triangle
The area of the rectangle: 9 • 2 = 18
The area of the triangle: 1/2 • 8 • 4 = 16
The total area: 18 + 16 = 34
He needs 34 m square of grass
So, the equation is y=mx + b and you want to solve for b to find the y intercept.
-5=2(4) + b
-5=8+b
subtract the 8
-13=b
the equation is y = 2x - 13
2 Gallons. 4 Quarts go Into 1 Gallon