small fixes

components/explorers/fraction-operation-explorer.tsx

@@ -174,8 +174,12 @@ function FractionBar({
   );
 }
 
-export function FractionOperationExplorer() {
-  const [op, setOp] = useState<Operation>("add");
+export function FractionOperationExplorer({
+  initialOperation = "add",
+}: {
+  initialOperation?: Operation;
+} = {}) {
+  const [op, setOp] = useState<Operation>(initialOperation);
   const [n1, setN1] = useState("1");
   const [d1, setD1] = useState("3");
   const [n2, setN2] = useState("1");