We know Amber worked 4 hours on a Saturday, so she earned 4*£10= £40 that day. The rest of the money, which is £180-£40=£140, she must have earned it during the week. Knowing she earns £7 per hour, this will give us £140:£7=20 hours. Adding up the hours during the week and the ones from Saturday, we get 20+4= 24 hours..