Answer:
If a line is parallel with Another...
They will have the same Gradient or equal Gradient (m)
So for two parallel lines
m=m'
So the gradient of the second or other line would be Same
Now
y= -3x + 10
comparing with
y= mx + c
m = -3
So the other line would have the same gradient.
from the options provided in the comment section...
y= -3x + 12
Is your Most probable answer cos it has the same gradient