small fixes

components/explorers/decimal-arithmetic-explorer.tsx

@@ -227,8 +227,12 @@ function ColumnArithmetic({
   );
 }
 
-export function DecimalArithmeticExplorer() {
-  const [op, setOp] = useState<DecOp>("add");
+export function DecimalArithmeticExplorer({
+  initialOperation = "add",
+}: {
+  initialOperation?: DecOp;
+} = {}) {
+  const [op, setOp] = useState<DecOp>(initialOperation);
   const [aInput, setAInput] = useState("12.45");
   const [bInput, setBInput] = useState("3.7");
   const [error, setError] = useState("");