light glows for every 15 seconds . how many times did it between 1 : 57 : 58 and 3 : 20 : 47 am
"the diff in sec between 1 : 57 : 58 and 3 : 20 : 47 is 4969 sec , 4969 / 13 = 331 . so total 332 times light ll glow answer : b"
divide(add(add(const_2, 47), multiply(add(20, add(const_2, const_60)), const_60)), 15)