Answer:

Step-by-step explanation:
The first step to solving this problem is verifying if this sequence is an arithmetic sequence or a geometric sequence.
This sequence is arithmetic if:

We have that:




This is not an arithmetic sequence.
This sequence is geometric if:




This is a geometric sequence, in which:
The first term is 40, so 
The common ratio is
, so
.
We have that:

The 10th term is
. So:



Simplifying by 4, we have:

Answer:
4
Step-by-step explanation:
20 x 4 = 80
so 1 per 20 minuets,and 4, 20 min. magazines would mean he needs 4 to make it to 80
<span>(2d - 5)(2d - 4) = 4d^2 - 2d x 4 - 5 x 2d + 20 = 4d^2 - 18d + 20
Answer is B
Hope it helps! </span>