Hello i have a question for my homework and i am struggling in solving it i would appreciate it if you can help me on this question

The national union of wheeltappers finds that the cost of transporting its members to a picket line is directly proportional to the number of pickets.

If it costs £55 to transport 20 pickets what will be the cost of transporting 35 pickets?

If the cost was £137.50 how many pickets were transported?

Thank you for all your help