343 + what =979

P. S i need a 5th grade explanation please

Which property was used to simplify the expression? 3c+9 +4c=3c+4c+9

How many liters of peroxide should be added to 12 liters of an 8% peroxide solution so that the resulting solution contains 16% peroxide?   original added new amount of peroxide 0.96 liters x 0.96 + x amount of solution 12 liters x 12 + x 0.18 liter 1.14 liters 1.92 liters 2.10 liters

The ratio of the height of two similar cylinders is 4 to 3 what is the ratio of their volumes