26 I think (i'm not sure please correct me.)
It is A. 186
11*6=66 and 24(which I found by adding 11+7+6) *5=120
120+66=186
The given equation is

It is given that , when x=0, f(x)=36
Substituting these values

So the missing value of a is 2 .
Explanation:
Discount = 20%
The cost of 5 notebooks = $10
The cost of 1 notebook before applying discount = $10/5 = $2
Applying the discount on the original price:
Discount = $10 × 20% = 10 × 0.20
Discount = $2
The sales price of the 5 notebooks = original price - discount
The sales price of the 5 notebooks = $10 - $2
The sales price of the 5 notebooks = $8
The sales price of 1 notebook = $8/5
The sales price of 1 notebook = $1.6
The amount saved per notebook = The cost of 1 notebook before applying discount -
$2 -