The affirmative answer to لَوْ commonly begins with لَـ. This marks the answer clause clearly.
لَوْ زَرَعْتَ لَحَصَدْتَ
Condition: زَرَعْتَ — you had sown.
Answer: لَحَصَدْتَ — you would have reaped.
لَوْ دَرَسْتَ لَنَجَحْتَ
If you had studied, you would have succeeded.
The rule says “commonly,” not “in every possible sentence.”