Can anyone help a fellow out ?

Use the elimination method to solve the system of equations -x+5y=-4 and 4x+3y=16

You and a friend went to the movies.you spent half your money on tickets. then you spent 1/4 of the money on popcorn, $2 on candy, and $3 on a soda. if you have $1 left, hiw much money did u take to the movies?

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.