Please help me solve this word problem.

Question

After 8 test, Sally's average in biology is 68. Her teacher said she could drop the two lowest test grades, which are the same. Her new average is 72. What were the grades of the two lowest?

Answer 1

8*68=544 total points

(544-x-x) means that she now has only 6 test grades

with the 6 test grades her average is 72

(544-x-x)/6=72

(544-2x)/6=72

(544-2x)=6*72

544-2x=432

544-432=2x

112=2x

x=112/2

x=56 were the 2 lowest grades