Update solution.md

I've added the solution here because the reader is obliged to go to the sandbox to see the solution, which has not happened till now in the course. And even there's already a link for doing that just above.

1-js/04-object-basics/01-object/8-multiply-numeric/solution.md

@@ -0,0 +1,19 @@
+``` js run
+
+// before the call
+let menu = {
+  width: 200,
+  height: 300,
+  title: "My menu"
+};
+
+function multiplyNumeric(obj) {
+  for (let key in obj) {
+    if (typeof obj[key] == 'number') {
+      obj[key] *= 2;
+    }
+  }
+}
+
+alert(menu); 
+```