Hello,
Start by writing out the area formula's for both a triangle and a rectangle.
Triangle: Area=(1/2)Base x Height Call this area A(T)
Rectangle: Area=Base x Height Call this area A(R)
Ultimately, we are trying to find the difference between the two so A(T) - A(R) = ?
Start by finding the A(T). We are given that the base=(3y-1) and the height=6y. According to our formula above, A(T)=(1/2)(3y-1)(6y). Once you foil this all out you get A(T)=9y^2 -3y
Next, find A(R). Again, follow the formula from above with the given info from the problem. A(R)=(5y-7)(y+4). Foil this out and combine like terms to get A(R)=5y^2 +13y-28
Now we can subtract the two and find that A(T) - A(R) = 4y^2 + 10y - 28. Or answer D.
