A marketing group developing online ad space is offering two payment options:

Option 1: $210 set up fee plus $10/inch of the ad
Option 2: No set up fee but $25/inch of the ad
Let x = inches of the proposed ad, for example, x = 2 for a column ad that is 2
inches long.
a) Write a mathematical

Not sure what type of "mathematical...." you want.

The cost will be equal if:

210 + 10x = 25x