Show me steps to solve: A complex airborne navigating system incorporates a sub$-$assembly which unrolls a map of the flight plane synchronously with the movement of the aero$-$plane. This subassembly is brought on very good terms from the sub$-$contractor $,$ but is not always in perfect adjustment on delivery $.$ The subassemblies can be re adjusted on to guarantee at the cost of SR $500$ per sub$-$assembly $.$ It is not, however, possible to distinguish visually those sub$-$assemblies that need adjustment. Alternatively $,$ the sub$-$assemblies can each be tested

electronically at a cost of SR$100$ per sub$-$assembly tested

$.$ Past experience shows that about $30\%$ of those

supplied are defective, the probability of the test

indicating a bad adjustment when the sub$-$assembly is

faulty is $0\mathrm{.}8,$ while the probability that the test indicates

a good adjustment when the sub$-$assembly is properly

adjusted is $0\mathrm{.}7.$ If the adjustments is not made and the

sub$-$assembly is found to be faulty when the system has

its final check, the cost of subsequent rectification will

be Sr$1400.$ Draw up an appropriate decision tree to

show the alternatives open to the purchaser and use it

to determine his appropriate course of action $.$