I neeed help with middle school math

Which expression shows the sum of the polynomials with like terms grouped together

Solve the system of equations using the linear combination method. {4x−3y=127x−3y=3 enter your answers in the boxes.

In july, the average temperature in one us city was 29°c. by december, the average temperature had fallen by 29°c. explain why the average temperature in december was 0°c.