Find the missing side 3 and 4.​

During a bike challenge riders have to collect various colored ribbons each 1/2 mile they collect a red ribbon each eighth mile they collect a green ribbon and each quarter mile they collect a blue ribbion wich colors of ribion will be collected at the 3/4 markrer

Which expression is not a polynomial?

Prove that the value of the expression 7^8–7^7+7^6 is divisible by 43.