The answer is: " 13√7 " .
_________________________________________
Explanation:
_________________________________________
" √63 " = √9 √7 = " 3√7 " .
_________________________________________
" √28 " = √4 √7 = " 2√7 " .
_________________________________________
" 5√28 " = " 5 * 2 * √7 = " 10√7 " .
_________________________________________
→ " 5√28 " + " √63 " ;
= " 10√7 " + " 3√7 " ;
= " (10 + 3) * (√7) " ;
= " 13 √ 7 "
________________________________________________
The answer is: " 13√7 " .
________________________________________________