feat : Added the solution to Finding Missing Digit for Github Externship

Solution.js

@@ -1 +1,61 @@
-// Write your code here
+class FixEquation {
+    //this function extracts the operands for us , i.e A , B , C , D
+	getAllOperands = (equation) => {
+		let operands = equation.split(' ');
+		operands = operands.filter(
+			(operand) =>
+				operand !== '+' &&
+				operand !== '*' &&
+				operand !== '='
+		);
+		return operands;
+	};
+
+    //This function finds the Operands containing the Question Mark
+	getIncompleteOperand = (operands) => {
+		let res;
+		operands.forEach((operand, i) => {
+			if (operand.includes('?')) res = i;
+		});
+		return res;
+	};
+
+    //Function tot find the value of ?
+	findMissingDigitUtil = (operands, incompleteOperand) => {
+		switch (incompleteOperand) {
+			case 0:
+				return eval(`(${operands[3]} - ${operands[2]}) / ${operands[1]}`);
+			case 1:
+				return eval(`(${operands[3]} - ${operands[2]}) / ${operands[0]}`);
+			case 2:
+				return eval(`${operands[3]} - ${operands[0]} * ${operands[1]}`);
+			default:
+				return eval(`${operands[0]} * ${operands[1]} + ${operands[2]}`);
+		}
+	};
+
+	findMissingDigit = (equation) => {
+		const operands = this.getAllOperands(equation);
+		const incompleteOperand = this.getIncompleteOperand(operands);
+		let result = this.findMissingDigitUtil(operands, incompleteOperand);
+		result = result.toString();
+		return result.length != operands[incompleteOperand].length
+			? -1
+			: result.charAt(operands[incompleteOperand].indexOf('?'));
+	};
+}
+
+// tests are in the form of A * B + C  = D
+const tests = [
+	'42 * 47 + 2 = 1?76',
+	'4? * 47 + 2 = 1976',
+	'42 * ?7 + 2 = 1976',
+	'42 * ?47 + 2 = 1976',
+	'2 * 12? + 2 = 247',
+];
+
+const callFixEquation = new FixEquation();
+tests.forEach((test) => {
+	console.log('Equation: ', test, '\n');
+	console.log('Returns: ', callFixEquation.findMissingDigit(test), '\n');
+});