Fuel Cycle Class

[nanners]

A nuclear power plant uses 87 tons of uranium in its core. The first core consists of three equal batches with enrichments of 2.5%. 2.9%, and 3.1%. For subsequent cycles, the reactor uses batches with enrichments equal to 2.6% and 3.2% in alternate years. One-third of the core is discharged each year and is replaced by new fuel. Assume a 30-year lifetime and 0.2% tails during the life of the plant. Calculate the number of SWUs needed for the first core. The number of SWUs needed every year after the first cycle. The number of SWUs needed total over the life of the plant.
I've calculated the three separation potentials for the 2.5% enrichment and the feed factor to obtain the product enrichment in kg.

My question is if I use the 87 tons to calculate the SWU or if I'm supposed to use 29 tons since its in 3 equal batches? Also how to incorporate the subsequent batches with enrichments 2.6% and 3.2%?

I have the equation to calculate the SWU in a lifetime but I'm not sure what separation values to use since they're alternating. I can do the calculations, I just need clarifications.

Thanks!