5x - y + 15 = 0
Explanation:
The x-intercept occurs at (-3, 0). The other line also goes through this point and has a slope of m = 5 so the equation of this line is
y = 5x + k
where k is the y-intercept. Since this line goes through (-3, 0), substitute this into our equation and we'll get
0 = 5(-3) + k or k = 15
Our equation then becomes
y = 5x + 15
or in standard form, it is
5x - y + 15 = 0