Since we have #x# raised to itself and to a number, there is no simple calculation to perform.
One way of finding the answer is an iteration method.
#x^x+x^7=326592#
#x^7=326592-x^x#
#x=(326592-x^x)^(1/7)#
Let #x_0=5#
#x_1=(326592-5^5)^(1/7)=6.125#
#x_2=(326592-6.125^6.125)^(1/7)=5.938#
#x_3=(326592-5.938^5.938)^(1/7)=6.022#
#x_4=(326592-6.022^6.022)^(1/7)=5.991#
#x_5=(326592-5.991^5.991)^(1/7)=6.004#
#x_6=(326592-6.004^6.004)^(1/7)=5.999#
#x_7=(326592-5.999^5.999)^(1/7)=6.001#
#x_8=(326592-6.001^6.001)^(1/7)=6.000#
#x_9=(326592-6.000^6.000)^(1/7)=6.000#
Though you may do yours to 1 ot two decimal places and do the first 5 iterations, giving a good approximation.