что означают выражения 18-3 и 18+(18-3)

описать море с помощью глаголов-сказуемых

Last weekend my mother and father [go]____ to the country [see]___my grandfather and grandmother.I [de]___at home alone.I [play___computer games, [do]___my Maths and foreign language homework, [draw]____a nice picture for my Art lesson on Monday.Soon I [feel]____hungry.But there [be]____nothing [eat]____in the fridge.So I [go]___to the shop.I [buy]_____lots of food:it's nice [be]_____at home alone.Next Sunday my family [go]_____to the friends.And I [stay]___at home again.