# If $s$ and $p$ are respectively the sum and the product of the slope of the lines $3x^2-2xy-15y^2=0,$ then $s:p=$
$\begin {array} {1 1} (a)\;4:3 & \quad (b)\;2:3 \\ (c)\;3:5 & \quad (d)\;3:4 \end {array}$