In this case, which is the offer and which is the acceptance to create an agreement of a contract? Is there an agreement?

Bikes Pty Ltd is the manufacturer of a new mountain bike called the Challenge. It is popular with professional mountain bike racers both because of its low weight having a carbon fibre frame, and its renowned reliability. The reliability of the Challenge comes from its innovative suspension system on both front and back wheels. However, this system makes the bike very expensive and it has not found a market with general consumers. Bikes Pty Ltd is looking to grow their business and determines that the way forward is to introduce a reduced cost mountain bike, to be called the Mountaineer. Consulting Engineers were the engineers that designed the original Challenge. Roger has just been employed as a consultant at Consulting Engineers, who are now renowned experts in the field of bike design. Roger has an automotive engineering background and has never worked on the design of a bike. Nonetheless, he is appointed chief engineer. One day Roger receives the following email from Bikes Pty Ltd. "We are going to produce a new bike, the Mountaineer, your company was involved in the design of the Challenge. It is a very small update and only involves a change to the suspension, everything else is the same as the Challenge. We need to reduce the cost of the suspension. Are you able to assist us? Roger replies: "No problem, I will start work immediately. Roger then starts working on the design and after a month has come up with a first prototype design with a lighter and cheaper suspension system. He sends the design through to Bikes Pty Ltd along with an invoice totaling $15,000 for work completed. Unbeknownst to Roger Bikes Pty Ltd has entered into an agreement with another design company for the design of the Mountaineer