I don't think the answer given is correct. Ppm is parts per million. From a percentage concentration, calculating ppm is just a matter of multiplying by 10000 (since % is parts per hundred). Given that, and assuming you've provided the correct number as per the question, I get 7ppm. Can you check that the question states 0.0007% and not 0.00007%?

Parts per million

0.00007% means 0.00007 per 100 (percent)

Thusly 0.00007/100 = 0.0000007

0.0000007 * 1000000 = 0.7 Parts per million

This is correct, but the OP doesn't give 0.00007% as the value.