diff --git a/modules/12_cpp20/src/span.cpp b/modules/12_cpp20/src/span.cpp
index eae3ad1..33d1224 100644
--- a/modules/12_cpp20/src/span.cpp
+++ b/modules/12_cpp20/src/span.cpp
@@ -1,21 +1,23 @@
 #include "span.hpp"
 
+#include <algorithm>
+#include <ranges>
+
 namespace cpp20 {
 
 auto span_sum(std::span<const int> data) -> int {
-    (void)data;
-    return 0;
+    return std::ranges::fold_left(data, 0, std::plus<>{});
 }
 
 auto first_and_last(std::span<const int> data) -> std::pair<int, int> {
-    (void)data;
-    return {0, 0};
+    return {*data.begin(), *(--data.end())};
 }
 
-auto make_subspan(std::span<const int> data, std::size_t offset, std::size_t count)
+auto make_subspan(std::span<const int> data, const std::size_t offset, std::size_t count)
     -> std::vector<int> {
-    (void)data; (void)offset; (void)count;
-    return {};
+    return std::views::drop(data, offset)
+        | std::views::take(count)
+        | std::ranges::to<std::vector<int>>();
 }
 
 }  // namespace cpp20