Genevieve forgot the last two digits of her four digit locker code the digit she has right now are 21 if the number is divisible by 5 x 6 in by seven what is genevieve's locker code

If a number is divisible by 5, 6, and 7, 

it's divisible by 5 x 6 x 7 = 210, the least 

common multiple of the numbers. So her number 

is a multiple of 210. The only 4-digit multiple 

is 210 that starts 210 _ is 2100, so that's her number.