Update marking.md

Author: chrisdavidmills

learn/tasks/grid/marking.md

@@ -29,15 +29,15 @@ I have used the shorthands below, however it would be correct for the student to
  grid-row: 2 / 4;
 }
 ```
-###Additional question
+### Additional question
 
-This extra question requires a little of research from the student. One way of achieving this would be to use `order` which we've encountered in the flexbox tutorial.
+This extra question requires a little bit of research. One way of achieving this would be to use `order`, which we've encountered in the flexbox tutorial.
 ```
 .item1 {
  order: 1
 }
 ```
-Another valid solution with `z-index`:
+Another valid solution is to use `z-index`:
 ```
 .item1 {
  z-index: 1;