PLEAS CAN SOMEONE HELP ME WITH THIS Reggie was solving a system of equations. after manipulating them, he decides to add the two equations shown below together to eliminate the variable x. what property justifies this?

please show work :)

6x + 5y = 17
-6x + 2y = 4

thank you to anyone who helps me :)))

Are carpet coast $15 per square metre. the total delivery charge is $21 peter buys n squared metres of carpet what is the expression which represents the total cost in $

Simplify 24÷(-2)(3)+7 a. -29 b. 3 c. 11

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.