ORF is a sequence encoding amino acids, generally

from 5' to 3' direction

starting with ATG, TAA, TAG or A sequence that ends with TGA and the number of nts is a multiple of 3

From the meaning of the question, you may also need to consider the ORF that exists on the complementary chain

For example, in the question

The complementary strand of 5'-TTATAGTTTCCCGGAAGCATCTGCCAT-3'

:

3'-AATATCAAAGGGCCTTCGTAGACGGTA-5'

It is also an ORF