After reading 80% of her emails in her inbox, danette still has m unread emails.

and

Step-by-step explanation:

1. Let's imagine that you have 100 e-mails unread. When you read 80% of these e-mails you have the following amount unread:

e-mails

2. If you substitute 20 e-mails into the equations shown above, you will obtain the original amount:

answer :  option A  and B

After reading 80% of her emails in her inbox, Danette still has M unread emails

M unread emails

Let x be the number of emails before reading

80% of emails are left in the box. So, 0.08x  emails are left in the box

Now we make an equation

number of emails - 80% of unread emails= number of unread mails

x  - 0.08x = M

Now we factor out x

x ( 1- 0.08) = M

So

or