light glows for every 16 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 / 16 = 310 . so total 311 times light ll glow answer : a"
divide(add(add(const_2, 47), multiply(add(20, add(const_2, const_60)), const_60)), 16)