If for one second we have to reserve 25 frames to find length of the movie we have to divide 1750 by 25, so
1750:25=70 [seconds] - its the result
To better understand lets think that u have 8 piece of cake and u want to give every person 2 piece. To find how many person u can invite u can divide 8 by 2. The answer is 4 here ofc.