A decorative platform is built by stacking horizontal layers of identical wooden blocks. The bottom layer uses 60 blocks, and each successive layer uses 5 blocks fewer than the layer immediately below it. Layers continue to be added until the number of blocks in a layer would become zero or negative.
Use this setting to answer the questions below.
(i) How many blocks are used in the 15th layer?
(ii) Find the total number of blocks required to build the first 15 layers.
(iii) If the builders have at most 1000 blocks available, what is the maximum number of complete layers that can be constructed?