00:02
So for this problem, we're given the cost function, cost as a function of the number of units, and we're given the number of units function as a function of time.
00:14
Excuse me, so what we want to do is find the cost as a function of time.
00:18
So the composition, c of x, will give us cost as a function of time.
00:23
So we're going to substitute the inside function, number of units, into the cost function.
00:29
And we get 60 times 50t plus 700.
00:35
So that would be 300t plus 750.
00:41
And as i said that the interpretation of that is we have cost as a function of time.
00:54
So for part b of the problem, what we want to do is find the cost at a time of four hours.
01:00
So we can just substitute four into our new equation, 300 times 4 plus 750...