Translation:This shirt is more expensive than that shirt.
Here and elsewhere a good native speaker editor is needed. The app.allow for some "flexibility" too...there if often times more than one correct answer.
I answered as "than that 1." Since the similar one about pants was incorrect when answered as "than that pair" and the correct answer was "than that 1". The answers are a bit inconsistent and need rounding out in the flexibility.
Just a note on English grammar... If 'one' is being used as a pronoun, you shouldn't use a numeral '1'.