You can use the method: part = percent • whole.
You percent is 70% and whole is 20. Your part is x since that's what you need to find.
You turn 70% into a decimal which is .70, and multiply .70 by 20. This will give you 14, therefore you she sold 14 candy bars. Now you need to subtract how much she sold from how much she needs to sell. 20 minus 14 is 6. She needs to sell 6 more candy bars.
