Need to make own equation then I'm pretty sure find derrivitive then use restrictions to find the max or something

2. A power plant and a newly constructed factory are on opposite banks of a straight river (see diagram below). A cable must be run from the plant to the factory. Laying cable on land costs $9/m, but underwater, the cost jumps significantly to $36/m. How should the cable be laid in order to minimize its cost? [T/C 9] 300 m F P - power plant 120 m RIVER F - factory P + cost