Complex sentence: Neoclassical economists assumed that there was no real problem here--just add up the money value of all these different capital items to get an aggregate amount of capital (while correcting for inflation's effects).
Split into simpler sentences: Neoclassical economists assumed that there was no real problem here. They said: just add up the money value of all these different capital items to get an aggregate amount of capital (while correcting for inflation's effects).