Ok
2x + y - z = 7
-2y +3z = -15
x + 2y - 5z = 17
combine 2nd 3rd
x - 2z = 2
x = 2z + 2
double first statement
4x + 2y - 2z = 14
combine with second statement
4x + z = -1
substitute 2z + 2 for x
8z + 8 + z = -1
combine like terms
9z + 8 = -1
sub 8 from both sides
9z = -9
divide both sides by 9
z = -1
substitute -1 for z in second statement
-2y - 3 = -15
add 3 to both sides
-2y = -12
divide both sides by -2
y = 6
substitute -1 for z into the fifth statement
x = -2 + 2
x = 0
50+2x+10+3x+15=180
50-10+15=55
2x+3x=5x
55+5x=180
5x=180-55
5x=125/5
x=25
That's an equation that describes a linear and proportional relationship between 'x' and 'y'. The graph of that equation is a straight line through the origin whose slope is. 1/3 .