A spherical tank for storing gas under pressure is 24 m in diameter and is made of structural steel 15 mm thick. If the yield stress of the material is 250 N/mm² and factor of safety 2.5. Determine, (i) Maximum permissible internal pressure, assuming that the welded seams between the various plates are as strong as solid metal and. (ii) Permissible pressure, if the seams are 75% as strong as solid metal.