Find X. Please show step by step.

no links or unhelpful answers.

Two customers went to a post office. first customer paid $12 for 14 and 5 envelopes the second paid 24.80 for 10 postcards and 15 envelopes. what is cost of each envelope?

Find the least common denominator for thesetvo rational expressions.n^2/n^2+4n+4 -3/n^2+7n+10

Ineed with question three. i don't understand how i'm supposed to achieve 3 marks.