Add ReturnOnInvestment to maths

Author: InukaWijerathna

maths/return_on_investment.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+# Calculates Return on Investment (ROI) as a percentage.
+# ROI measures the profitability of an investment relative to its cost.
+#
+# Formula: ROI = (Gain - Cost) / Cost * 100
+# Reference: https://www.investopedia.com/terms/r/returnoninvestment.asp
+class ReturnOnInvestment
+  def self.call(gain_from_investment, cost_of_investment)
+    raise ArgumentError, 'cost_of_investment must be greater than 0' if cost_of_investment <= 0
+
+    (gain_from_investment - cost_of_investment).to_f / cost_of_investment * 100
+  end
+end