How to find the angle between two lines given their slopes?

In the 30-60-90 triangle below side s has a length of and side r has a length

The graph represents the gallons of water in a water tank with respect to the number of hours since it was completely filled

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.