diff --git a/src/calculator.js b/src/calculator.js
index f41ea2af..924b58e7 100644
--- a/src/calculator.js
+++ b/src/calculator.js
@@ -1,8 +1,8 @@
 exports._check = (x, y) => {
-  if (typeof x !== "number") {
+  if (typeof x !== 'number') {
     throw new TypeError(`${x} is not a number`);
   }
-  if (typeof y !== "number") {
+  if (typeof y !== 'number') {
     throw new TypeError(`${y} is not a number`);
   }
 };
@@ -13,17 +13,17 @@ exports.add = (x, y) => {
 };
 
 exports.subtract = (x, y) => {
-exports._check(x,y);
+  exports._check(x, y);
   return x - y;
 };
 
 exports.multiply = (x, y) => {
-  exports._check(x,y);
+  exports._check(x, y);
   return x * y;
 };
 
 exports.divide = (x, y) => {
-exports._check(x,y);
+  exports._check(x, y);
   return x / y;
 };