Step 1: Identify the tense in direct speech.
The original statement is: “I am thinking of watching a film this weekend.”
Here, the verb tense is present continuous (“am thinking”).
Step 2: Apply the rule of tense change in indirect speech.
When reporting speech, if the reporting verb (e.g., “told”) is in past tense, the tense of the reported statement generally shifts back:
- Present continuous \(\Rightarrow\) Past continuous.
Step 3: Apply the change.
“I am thinking” \(\Rightarrow\) “he was thinking”.
Also, “this weekend” \(\Rightarrow\) “that weekend”.
Step 4: Construct the indirect sentence.
Thus, the correct indirect speech is:
\[
\text{Rafi told Mary that he was thinking of watching a film that weekend.}
\]
Final Answer:
\[
\boxed{\text{was thinking}}
\]