Answer:
Area of the shaded region= 
Step-by-step explanation:
Area of the shaded region= Area of the triangle- Area of the rectangle
Dimensions of the triangle:
Base= 40 inch
Height= 40 inch
Area of a triangle=

Area of the rectangle= Length*Width
Length=30 inch
Width=10 inch
Area:

Area of the shaded region= 
Answer:
(4, 6)?
Step-by-step explanation:
Im not sure you didn't give much info
So, how much acid is there in 6 gallons? well is 20% acid or (20/100), so the amount of acid in it just (20/100) * 6 or 1.2, the rest is say water.
now, if we want a 90% solution, and say we add "y" gallons, how much acid is in it? well (90/100) * y, or 0.9y.
now let's add "x" gallons of pure acid, now, pure acid is just pure acid, so is 100% acid, how much acid is there in it? (100/100) * x, or 1x or just x.
we know whatever "x" and "y" amounts are, they -> x + 6 = y
and we also know that x + 1.2 = 0.9y