let

b = the number of boys

g = the number of girls

b + g = the total number of students

68% of John's school are boys

0.68(b + g) = b

there are 180 more boys than girls

b = 180 + g

by solving the system

0.68(b + g) = b

b = 180 + g

we find

b = 340 boys

g = 160 girls

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b + g = 340 + 160 = 500 students

there are 500 students in total.