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Part n 13)
we have that
3x+y=-2> multiply by both sides> 6x+2y=-4> equation 1
x-2y=4---> equation 2

add equation 1 and equation 2
6x+2y=-4
x-2y=4

7x=0> x=0
x-2y=4> 0-2y=4> y=-4/2> y=-2

the solution is the point (0,-2)

the answer part n 13) is the option B
there is exactly one solution (0,-2)

Part 14)

let 
x> the number of years
y> height of the tree in ft

case a) y=8+x> equation 1
case b) y=10+(1/2)x> equation 2
equate equation 1 and equation 2
8+x=10+(1/2)x> multiply by 2 both sides> 16+2x=20+x
2x-x=20-16
x=4 years
for x=4 years
case a) y=8+x---> 8+4> y=12 ft
case b) y=10+(1/2)*4> 10+2---> y=12 ft

the answer part 14) is
4 years

Part 15)
let
x> number of adult tickets
y> number of child tickets

we know that
x+y=14> x=14-y> equation 1
9x+5y=110> equation 2

substitute equation 1 in equation 2
9*[14-y]+5y=110> 126-9y+5y=110
9y-5y=126-110
4y=16
y=4
x+y=14> x=14-y> x=14-4> x=10
so
number of adult tickets is 10
number of child tickets is 4

the answer Part 15) 
number of adult tickets is 10