Can anyone provide a solution to this problem?

Jabari is power washing houses for a summer job. for every job, he charges an initial fee plus $30 for each hour of work. his total fee for a 4 -hour job, for instance, is $170 . jabari's total fee, f, for a single job is a function of the number, t, of hours it takes him to complete the job. write the function's formula.

X+ y = 5 ; x - y =3 solve using linear combination

Answer! if you don’t mind, can you explain