i think this is it for question 4
<a href="http://www.codecogs.com/eqnedit.php?latex=Since \, the\, two\,lines\,are\,parallel\,\\\therefore m(L_2)=m(L_1)\\\therefore y-0=m(x-Q)\\y=m(x-Q)\\ at\,y\,intercept\,x=0\\y=m(0-Q)\\\therefore y=-mQ \\ Hence\,y\,intercept\,of\,L_2\,is (0,-mQ)"...