What is the measure of DAB

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?

F(x)=x/2-2 and g(x)=2x^2+x-3 find (f+g)(x)

The formula for the lateral area of a right cone is la = rs, where r is the radius of the base and s is the slant height of the cone. which are equivalent equations?