4x – y = 7 3y – 12x = –21

The table shows the webster family’s monthly expenses for the first three months of the year. they are $2,687.44, $2,613.09, and $2,808.64. what is the average monthly expenditure for all expenses?

Ammonia molecules have three hydrogen atoms and one nitrogen atom.how many of each atom arein five molecules of ammonia

In triangle △abc, ∠abc=90°, bh is an altitude. find the missing lengths. ah=4 and hc=1, find bh.