Question 511023
Use
nCr=n!/r!(n-r)!

Given
n=7, r=4
nCr=n!/r!(n-r)!
nCr=7!/4!(7-4)!
nCr=7!/4!3!
nCr=7*6*5*4!/4!3!
Cancel our 4!
nCr=7*6*5/3!
nCr=7*6*5/3*2*1
nCr=210/6
nCr=35

35 Combinations.