(D) 20 metres East, then 20 metres North.
To solve this, just make sure that there is enough numbers on each to cancel each other out.
Matt walks 30 metres east, and 50 metres west, which means that he needs to walk another 20 metres east to get back to where he was.
Matt walks 70 metres south, and 50 metres north, which means that he needs to walk another 20 metres north to get back to where he was.
This means that (D) is your answer
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hope this helps