Could a quadrilateral have 4 obtuse angles? why?

A50% increase followed by 33 1/2% decrease

How many liters of peroxide should be added to 12 liters of an 8% peroxide solution so that the resulting solution contains 16% peroxide?   original added new amount of peroxide 0.96 liters x 0.96 + x amount of solution 12 liters x 12 + x 0.18 liter 1.14 liters 1.92 liters 2.10 liters

y=2x−1 5x−4y=1 is (1,1)(1,1) a solution of the system?