Asurvey conducted in a school showed that 65% of the students walked to school. the remaining students took buses to school. the ratio of students who took buses to those who took public buses was 4: 3. there were 360 more students who walked than took buses. how many students took public buses to school? explain everything you did or just write your equations.

I fear that there is an error copying your assignment.  
65% of the students walked.  Are all of the other students on buses?  Are there both public buses AND private buses?
Assuming that you need to know BOTH kinds of buses, try this:

65% of the students walked, so since 100% - 65% = 35% then this means that 35% of the students were on buses.
Since we know that there are 360 more walkers than bus riders, then one equation we know is:  65% of S = 360 + 35% of S  (let S = total # of students)
              .65 S     = 360 + .35 S
            - .35 S     =        - .35 S      Subtract .35 S from both sides
              .30  S    =  360                 Divide both sides by .30 (or .3)
                .30           .30
                      S   =  1,200  so we know that this is the total number of students, but that is not what was asked.  
They want to know how many are on buses and specifically how many are on public buses, if I read this correctly.
   Since the walkers = 65% of 1,2000 and we know of means TIMES, then
                                  .65 (1,200) =  780 walkers
 1,200 total students minus 780 walkers = 420 bus riders

Now, if there is not a misprint and we really have to figure out the public bus riders as compared to the private bus riders, then remember the ratio from above in the question:   4 bus: 3 public buses
Now if I read this right, that means that 3/4ths of the bus riders were on public buses
so 3/4 of 420 means 3/4 times 420  = 3 times 105 = 315 public bus riders (which coincidentally leaves 105 private bus riders, but since they are private we don't know much about them.  Ha-Ha I made a lame joke.)

So your answer is 315 public bus riders

Maybe the answer is 20mm. all i really did was just multiply, which is obvious.