Question 58581
A) Since the cost of the taxi fare depends on the distance to the airport, you must include in your equation, a variable for the number of kilometres.  Let's call it K, so the equation would be:
a) y = $6.00 + $0.50(K)

b) y = $40.00 Since the cost for the limo. is fixed, there is no variable for the number of kilometres.

B) Resolve the equations?  Not quite sure what you are looking for here, but it seems that you would need to know the distance to the airport and this was not provided.
d) Based on the available information, I would advise Darell to take the taxi if the distance to the airport is less than 68 kilometres, but take the limo if it is more than 68 kilometres. 
Why? To find the distance at which the costs are the same, set the two equations equal to each other:

$6.00 + $0.50(K) = $40.00  Simplify this and solve for K. Subtract $6.00 from both sides.
$0.50K = $34.00 Divide both sides by $0.50
K = 68 kilometres.
So, at a distance of 68 kilometres, the taxi and the limo cost the same, so Darell should ride in comfort in the limo.
At a distance of more than 68 kilometres, the limo would still cost $40.00 and would thus be less expensive than the taxi.