Equation of the straight line

It is given that the straight line L1 passes through A(6,0) and B(6-a,3).
The straight line L2 is perpendicular to L1 and its y-intercept is -6.

(a) Find,in terms of a,the equations of L1 and L2.
(Express your answers in the general form.)

(b)Suppose the straight line L3: 2x+(5-a)y=c has positive slope and coincides with L2.

(i) Find the possible value(s) of a and c.
(ii) The two straight lines L3 and L4: px+2y=q do not intersect each other.
Suggest a possible set of p and q.


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