Answer:
1) y=-10x+50 (it's the only negative slope / going down option and it starts at x=0 y=50)
just substitute the x with a 9
y=-10*9 +50
y= -40
2) 0.5x +5 (only positive slop and starting point at x=0 is correctly 5)
we do need to substitute y this time, with 30 obviously
30 = 0.5x +5 |-5
25 = 0.5x | *2
50 = x
3) y=-2x +50 reasoning as before
substitute x with 4
y =-2*4 +50
y = -8 +50
y = 42
