How do I make this calculator work? (Ruby) : #I just wanted to work on one method then replicate it to the rest. which is why one method is really only done. (kinda)

puts "Welcome to My Calculator! "  

print "Please place in the numbers. "  

first_number = gets.to_i  

print "Second number. "  

second_number = gets.to_i  


puts "What operation? "  

operation_selection = gets  

if(operation_selection == "add")  

  addition_function  

  puts"#{result}"

end  


def addition_function
 result = first_number + second_number

end

def subtraction_function
  result = first_number - second_number

end

def divison_function
   result = first_number / second_number

end

def multiplication_function
  result = first_number * second_number

end

