Consider the idea of producing equivalent equations by adding the same number to both sides.
a. (i) Explain why the solution of an equation of the form ax+b=c remains unchanged when the same integer is added to both sides.
b. (ii) Without solving, predict whether the equations 6x−9=21 and 6x−9+4=21+4 have the same solution. Give a reason for your answer.
c. (iii) Verify your prediction in part (ii) by solving both equations and comparing their solutions.