I don't understand the "stop codon".. The answer is correct but I want to understand. The stop codon is TAA but you labeled it as TTA and TGA, in which the open reading frame $($ORF$)$ starts with ATG.

So$,$ the number of ORFs in the given DNA sequence is $1$

There is only one reading frame in the given DNA sequence, which is ATGCACCAGATCGCTTA.

$1$st step:

The start codon in RNA is AUG, and the stop codon is UAA, UAG, and UGA.