Question

They solved the paper with complete interest, ( Add a proper Question Tag) 

didn't they?

don't they?

do they?

did they?

​

Answer 1

$\Huge\bold{\underline{\underline{\red{Answer-}}}}$

$\huge \implies \large \rm\:Do. they$

Answer 2

$\huge\mathfrak{\underline{\underline{\red{Answer:-}}}}$

$\huge\implies\large\rm\:do\: they$