Answer
$\frac{7b}{5c^2}$
Work Step by Step
$42ab^2c=\underline2\times\underline3\times7\times \underline a\times b\times \underline b \times \underline c$
$30abc^3=\underline2\times\underline3\times5\times \underline a\times \underline b\times \underline c\times c\times c$
GCF=$2\times3\times a\times b\times c=6abc$
$\frac{42ab^2c}{30abc^3}=\frac{42ab^2c\div6abc}{30abc^3\div6abc}=\frac{7b}{5c^2}$
