Consider a firm with the following production function:

Question

q = (ak+bl)^(1/2)

The firm's total costs can be written as C = F + rk + wl

1. Calculate the firm's contingent factor demand. Illustrate it in a graph including the firm's isoquant map

2. Assume that r/w > a/b. Find the firm's long-run cost function.

This might be ridiculously easy but i just can't wrap my head around it.

For the first question i calculated the cost-minimization to:
w/r = b/a = RTS
Which would make the capital and labour perfect substitutes and the isoquant will be a straight line with the slope -b/a

But how do i find the contingent factor demand?
Normally the cost-minimization can be solved to find optimal values of l and k.

I'd really appreciate some help on this