Let lucy = l & neighbour= n l = n +4 l + n= 14 years substitute l with n +4 (n +4) + n = 14 2n +4 =14 n=5 years l = n + 4 lets substitute n with 5 l = 5 + 4 lucy = 9 years
Proofs are... well... just that. They are your proof for why a certain property works or what you did to show your work. So essentially, you just do math like normal, a proof is showing what you did and why it works.