Anewspaper charges a flat rate to place a 3-line ad in the classified section and then charges a per line fee for any additional lines. write an equation that gives

Let x equal the number of additional lines, z equal the charge per additional line, y equal the flat rate of 3 lines, and w the total price
since there is a flat rate of y for 3 lines you would put y
y
then since it charges a per line fee you can write z(x) to represent the total price of the additional lines.
finally you put it together to get y+z(x)=w