Using string class methods $($length$)$

Given the following declaration: String s $="7$ birds and $12$ cats";

Evaluate the expression: s$.$length$()$

Given two String variables, s$1$ and s$2,$ to determine if they are the same length, which of the following conditions would you use?

a$)($s$1.$equals$($s$2))$

b$)($s$1.$length$()$ equals$($s$2))$

c$)($s$1.$length$().$equals$($s$2.$length$())$

d$)($s$1.$length $()==$ s$2.$ length $()$