Answer:
The sentence that uses Standard English is: He said he would repay the money.
Step-by-step explanation:
By using the verb repay instead of pay, it's not necessary to add "back" to the sentence because it would just be redundant, as repay means to pay back. The sentence using "back" would have to be "He said that he would pay back the money". So the correct sentence is: He said he would repay the money.