Answer
(a) $3.7704$
(b) $0.3285$
Work Step by Step
(a) $ln(1+x^{3})-4=0$
$ln(1+x^{3})=4$
$(1+x^{3})=e^{4}$
$x^{3}=e^{4}-1$
Hence, $x=\sqrt[3]{e^{4}-1}\approx3.7704$
(b) $2e^{1/x}=42$
$\frac{1}{x}=ln(21)$
$x= \frac{1}{ln(21)}\approx0.3285$