Answer:
Grunkle Stan Pines baked a cake but forgot to add sugar; therefore, he took one bite and spit it out.
OR
Grunkle Stan Pines baked a cake but forgot to add sugar. Therefore, he took one bite and spit it out.
Explanation:
What is "Grinkle Stan Pines" ??
"Therefore" is not the appropriate word here, but your instructions say to correct only capitalization and punctuation errors.