The elements least likely to form bonds are found in which group? 15, 16, 17, 18

Find three consecutive numbers such that the sum of one-fourth the first and one-fifth the second is five less than one-seventh the third

Find the value of x. give reasons to justify your solutions! h ∈ ig

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.