$$23-1=22$$  $$22-10=12$$  $$12-1=11$$ 
Nancy has $23$ donuts. She gives one donut to Sana, and then Nancy has $10$ more donuts than Sana. At beginning, how many donuts does Sana have? 
a. $$10$$ 
b. $$11$$ 
c. $$12$$ 
d. $$13$$ 
e. $$14$$ 