Two lines are parallel when they have the same slope.
Line 1: px+3y+5=0
Line 2: 8x+2y−3=0
Converting Line 2 to slope-intercept form:
8x+2y−3=0
2y=−8x+3
y=−4x+23
Slope of Line 2 is −4.
Converting Line 1 to slope-intercept form:
px+3y+5=0
3y=−px−5
y=−3px−35
Slope of Line 1 is −3p.
For the lines to be parallel, their slopes must be equal:
−3p=−4
p=12
Therefore, p=12.