Try this solution:
1. Rule: if the equation of a line is 'y=kx+b', then line_1 will be parallel to line_2, when k_1=k_2.
2. According to the rule above the parameter 'k' of required line is (-5); the required equation is y=-5+b.
3. In order to calculate the parameter 'b', it need to substitute the coordinates (0;3) into the required equation, described in item 2 (y= -5x+b):
3= -5*0+b, then b=3.
4. If k= -5, b=3, then y= -5x+3