diff --git a/internal/exercises/solutions/04_constants/constants.go b/internal/exercises/solutions/04_constants/constants.go
new file mode 100644
index 0000000..b5ba196
--- /dev/null
+++ b/internal/exercises/solutions/04_constants/constants.go
@@ -0,0 +1,8 @@
+package constants
+
+import "math"
+
+// CircleArea calculates and returns the area of a circle with the given radius.
+func CircleArea(r float64) float64 {
+	return math.Pi * r * r
+}