Answer:
4
Explanation:
2/5*3000 = 1200 seniors
then
3000 - 1200 = 1800 students not seniors
therefore
4/5* 1200 = 960 do not like rock climbing
and
9/10** 1800 = 1620 also do not like it:
"how many students are in favor of this idea?"
subtract the "don't likes" from 3000
3000 - (960+1620) = 420 like rock climbing:
3x-x+2=4