Question

Write an equation whose graph is parallel to the graph of y= 0.5x - 10

Answer 1

0.5 is the gradient. Any equation with a gradient of 0.5 will be parallel to y=0.5x-10.
Any examples: y=0.5x+9.  y=0.5x-25.

Answer 2

                     y  =  0.5 x  +  (any number)

is parallel to the graph of  y = 0.5x - 10 .

If the (any number) happens to be  -10 ,  then the two lines
lie right on top of each other, and it looks like there's only
one line on the graph.