Monica and her parents spent 170 on new swimsuits monica swimsuits cost $35. her mom's swimsuit cost twice as much as monica's. how much did her dad's swimsuit cost?

Firstly, find your base. The cost of Monica's swimsuit is your base here. (35)
Next, find Monica's mother's swimsuit cost. (35 x 2 = 70)
After that, add the total cost of those two swimsuits. (105)
Finally, figure out what you have to add to the lesser side to make it even with the higher side. (170 = 105 + 65)
Monica's father's swimsuit would cost $65.
For reference, your equation could look like:
35 + 35 x 2 + X = 170