$4$ dollars and $50$ cents are equal to $450$ cents, so one scoop of ice cream costs $450 \div 3 = 150$ cents. $$3$$ dollars and $$60$$ cents are equal to $360$ cents, so one cookie costs $360 \div 2 = 180$ cents. Thus, Ala should pay $ 150 + 180 = 330$ cents for one scoop of ice cream and one cookie. $330$ cents are equal to $3$ dollars and $30$ cents, so the answer is $A$. 
Ala, Lenka and Miso went out for dessert. Lenka paid $$4$$ dollars and $$50$$ cents for three scoops of ice cream. Miso paid $$3$$ dollars and $$60$$ cents for two cookies. How much did Ala pay for one scoop of ice cream and one cookie? (2011 Math Kangaroo Problem, Level 3 - 4, Question \#6) 

  $3$~dollars and~$30$~cents 
  $4$~dollars and~$80$~cents 
  $5$~dollars and~$10$~cents 
  $6$~dollars and~$30$~cents 
  $8$~dollars and~$10$~cents 