Speed is given by

#"Speed" = "Distance"/"Time"#

From above

#"d = Speed × Time"#

#color(white)("d") = 3 × 10^8\ "m/s" × "1 week"#

#color(white)("d") = 3 × 10^8\ "m/s" × 1 cancel"week" × "7 days"/(1 cancel"week")#

#color(white)("d") = 3 × 10^8\ "m/s" × 7 cancel"days" × "24 hrs"/(1 cancel"day")#

#color(white)("d") = 3 × 10^8\ "m/s" × 7 × 24 cancel"hrs" × "60 min"/(1 cancel"hr")#

#color(white)("d") = 3 × 10^8\ "m/s" × 7 × 24 × 60 cancel"min" × "60 s"/(1 cancel"min")#

#color(white)("d") = 3 × 10^8\ "m"/cancel"s" × 7 × 24 × 60 × 60 cancel"s"#

#color(white)("d") = 3 × 10^8\ "m" × 604800#

#color(white)("d") = 1814400 × 10^8\ "m"#

#color(white)("d") = 1.8144 × 10^14\ "m"#

Light travelled #1.8 × 10^14\ "m"# (in 2 significant figures) in a week.