the correct answer is A
some scientific calculators have nPr button, you can enter 7 first then push shift (or 2nd) then nPr then 3, push= or enter
or you can use the formula nPr=n!/(n-r)!
7P3=7!/(7-3)!
=7!/4!=7•6•5•4!/4!
cancel 4!
then 7P3=7•6•5=210
note: the symbol ! means factorial
ex: 4!=4•3•2•1