4= √6x+15-x how do you solve this

Solve the equation using the given values: x= -2.5; y= -7.51. 2xy + 2x²

This is about circle theorems. someone asap : (

Asmall business produces and sells balls. the fixed costs are $20 and each ball costs $4.32 to produce. each ball sells for $8.32. write the equations for the total cost, c, and the revenue, r, then use the graphing method to determine how many balls must be sold to break even.