Added class problem-and-answer with margin on the bottom

common/lib/xmodule/xmodule/css/capa/display.scss

@@ -32,6 +32,7 @@ section.problem {
       display: inline;
   }
 
+
   div {
     p {
       &.answer {
@@ -321,6 +322,10 @@ section.problem {
     }
   }
 
+  .problem-and-answer {
+    margin-bottom: lh();
+  }
+
   .CodeMirror {
     border: 1px solid black;
     font-size: 14px;