Hey, please help. Can someone transfer the bottom equation in blue into vertex form please? I am so confused

What expression is equivalent to 42x-56y

The measure of one angle of an octagon is two times smaller that of the other seven angles. what is the measure of each angle?

Agroup of three friends order a combo meal which includes two slices of pizza and a drink each drink is priced at $2.50 the combined total of $31.50 how much is the cost of a slice of pizza