The first unit took $10$ hours and the eighth unit took $1\mathrm{.}25$ hours. What is the learning curve?

Question $23$ options:

a$)$

$50\%$

b$)$

$90\%$

c$)$

$80\%$

d$)$

$12\mathrm{.}5\%$

e$)$

None of these