$$35+29=64$$ 
The length of Amy\textquotesingle s string is $$35\text{cm}$$. The length of David\textquotesingle s string is $$29\text{cm}$$. What is the total length of both strings? 

a) $$54\text{cm}$$ 
b) $$49\text{cm}$$ 
c) $$64\text{cm}$$ 
d) $$65\text{cm}$$ 
e) $$66\text{cm}$$ 