Answer
$x\approx4.953$
Work Step by Step
As $f(x)$ is given, this is the output value therefore we have to calculate the input value of $x$.
$f(x)=2.5\times \ln x+3$
$7=2.5\times \ln x+3$
$4=2.5\times \ln x$
$\frac{4}{2.5}=1.6=\ln x$
$e^{1.6}=e^{\ln x}=x$ (Let both sides be exponents of the base e)
$x\approx4.953$
