Math help, linear equations

I need help with the following questions, I've tried them, but I keep getting decimal numbers.
x-2y=7
y=-x+1

and

x+3y=5
-2y+y=4

Also theres one question where we have to come up with the equations and graph it to find the Point of Intersection, I've got the equations down, but when I try to graph it, the lines dont intersect at all. The questions something like:
One party planner charges $20 for decorations and $8 an hour for a clown, another charges $25 for decorations and $6 an hour for a clown. I put the equations as: C=8x+20 and C=6x+25. Is this correct?

x - 2y = 7
y = -x + 1

x - 2(-x + 1) = 7

x + 2x - 2 = 7

3x = 9
x = 3
y = -2

x + 3y = 5
-2y + y = 4,
-y = 4
y = -4

x + 3(-4) = 5

x - 12 = 5
x = 17

Finally, your two equations for the party planner costs are correct.

(1) x-2y=7
y=-x+1

replace x with 1-y in first equation.
1-y-2y=7
1-3y=7
-3y=6
y= -2
and so x=3

(2) x+3y=5
-2y+y=4

from equation 2,
y=-4
x=17

(3) there';s something missing in the question, you cannot form equation from the given data.
Because, the costs of both party planning and clowns are fixed, no variable can be involved.

If the duration of the party is a variable, then equation can be,
20x+8y=0
6x+25y=0

where x is the duration duration of the party and y is the duration for clowns.