The Magic Box is offering a 15% discount on all items over $100. A wooden rocking horse at the store has a price of $140.
Which proportion below would be used to determine the discount amount?
a) 15/100 = x/100
b) 15/140 = x/100
c) 15/100 = x/140
d) 15/140 = 100/x
Plsss show work!

Long division setup showing an incomplete calculation. 12 is in the divisor, 6839 is in the dividend, and 5 hundreds and 6 tens is written in the quotient. 6000 is subtracted from 6839 to give 839. an unknown value represented by a box is being subtracted from 839. what number should be placed in the box to complete the division calculation?