Answer: 18 sixth graders
Explanation:
Let
x-----> the number of sixth graders in the band
y-----> the number of seventh graders in the band
we know that
-----> equation A
------> isolate the variable y
-----> equation B
Substitute equation B in equation A
x+ (1.5x) = 45
2.5x=45
x=45/25= 18 sixth graders