light glows for every 13 seconds . how many max . times did it glow between 1 : 57 : 58 and 3 : 20 : 47 am .
"time difference is 1 hr , 22 min , 49 sec = 4969 sec . so , light glows floor ( 4969 / 13 ) = 382 times . answer : c"
divide(add(add(const_2, 47), multiply(add(20, add(const_2, const_60)), const_60)), 13)