Roberto invested a total of $1, part at 6% and part at 9% . how much did he invest in the higher interest account if the total interest earned in one year was $810?

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.