Temperature drop in $$30$$ days $$=15^o$$C
Temperature drop in $$1$$ day$$=\dfrac{15}{30}=\left(\dfrac{1}{2}\right)^o$$C
Thus, there will be a temperature drop in next $$10$$ days $$=\dfrac{1}{2}\times 10=5^o$$C
Thus, there will be temperature drop of $$5^o$$C in the next ten days.