How many solutions does each system of equations have? Explain how you can tell,
a. x + y = 19
х- бу = 13

The? half-life of a radioactive substance is 20 years. if you start with some amount of this? substance, what fraction will remain in 120 ? years

Novak gives 9 packs of paper to a group of 5 students. if the group shares the paper equally how many packs of paper does each student get. write the a answer as a mixed number

Zahra wants the equation below to have an infinite number of solutions when the missing number is placed in the box.