A compound tube is formed by shrinking outer tube onto an inner tube with common

radius $150$ mm and thickness $25$ mm$.$ The shrinkage allowance is to be such that when

an internal pressure of $30$ MPa is applied the final maximum stress in each tube is to

be the same. Determine the value of this stress. What must have been the difference

in diameters of the tubes before shrinkage? E $=210$ GPa.