PLEASE HELP 5 EIGHTH GRADE ALGEBRA MATH PROBLEMS

1.
x=2y
-9x+4y=28

2.
y=-4x+5
8x-2y=-42

3.
3x+7y=-17
-3x+9y=-15

4.
6x+12y=36
4x-6y=-4

Aprojectile is thrown upward so that its distance above the ground after t seconds is given by the function h(t) = -16t2 + 704t. after how many seconds does the projectile take to reach its maximum height?

Is it greater than or less than7*3_9*2

How many grams the dog will eat in 3 days?