I 'm currently working on my exercise, the question is

Two lines

L1: 3x + y - 4 = 0 and

L2: 3x - y + 3 = 0 are given.

P (h,k) is a point on the line x - y + 1 = 0.

Suppose the distances of P from L1 and L2 are d1 and d2 respectively.

(a) Express k in terms of h.

>> I 've got it: k = h + 1

(b) Express d1 + d2 in terms of h.

>> That's easy as well.

ie. 1/(10)^(1/2) (|4h + 3| + |2h + 2|)

(c) When d1 + d2 is at the minimum, what is the value of h?

Find also the value of d1 + d2 and the coordinates of P at this instance.

>> This 's my problem. I got stuck and have no idea at all.

Please kindly help me.