So first, set up an equation for each shop, for the first one you can write 4x+28 (since it is 4 dollars for each cupcake and 28 dollars for the cake) and for the second shop you can write 55+x ( 55 dollars for cake and a dollar for each cupcake.) now you can set the 2 equations equal to each other because they want the number for cupcakes where the price will be equal. So 4x+28=55+x and then solve. I don’t want to completely tell you the answer but if you are stuck, you can tell me and I will gladly help.
