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You have to solve two equations for x and for b:
10x = e^(bx) and 10 = b*e^(bx)
Multiplying the second eqn by x and comparing it to the first eqn gives
e^bx = 10x = x*b*e^(bx)
It follows that 1 = x*b, so x = 1/b. A little more work will reveal that x = e/10.