គណិតវិទ្យាQCM

Sam-the-super-snail is climbing a vertical stone 1 meter high. He climbs at a steady speed of 30cm per hour, but each time the church clock strikes the shock causes him to slip down 1cm. The clock strikes the hour, so at 1 o'clock he would slip back 1cm, at 2 o'clock he would slip back 2cm and so on. If he starts to climb just after he clock strikes 3:00 pm; when will he reach the top?

(a). 3:50 pm

(b). 6:20 pm

(c). 6:50 pm

(d). 7:20 pm

(e). None of the above.