If you’re asking for the cost of the drink, the drink would be $1. This is because 2 sandwiches would cost $10 and that means 1 sandwich would make it $5. If 2 sandwiches cost $10, the remaining $2 in the $12 dollars would be the drinks. 2 drinks for $2 would make 1 drink for $1. So the cost of 5 drinks is $5 or $1 per drink.
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The only way to solve if it is equal to something
assuming that the teacher wanted you to make it equal to zero do
0=-3x^2-21x-54
remember if we can do
xy=0 then assume x and y=0
so factor
0=-3x^2-21x-54
undistribute the -3
0=-3(x^2+7x+18)
remember 0 times anything=0 so
x^2+7x+18 must equal zero
use quadratice formula which is
if you have
ax^2+bx+c=0 then
x=

x^2+7x+18
a=1
b=7
c=18
x=

x=

x=

i=√-1
x=

the zerose would be
x=

or
Answer is 41 miles total
Equation is (2miles x 7) + (3 miles x 9) = total
14 + 27 = total miles
41 = total miles
1) (-7,2)
y=2, -x+4=11, -x=11-4=7, x=-7
2) (-3,4)
-x+2y=11
y=4, -x+8=11, -x=3, x=-3
3) (1,6)
-x+2y=11
y=6, -x+12=11,-x=-1, x=1
Check image below for answer!