break them apart put 18 into 10 and 8 and multiply it by 30 10 x 30 equals 300 30 x 8 equals 240 add them up you get 540 do the same with next one break 15 into 10 and 5 multiply 20 by 5 and you get 100 multiply 20 by 10 and you get 200 add them up and you get 300 now add the final numbers up and you get 840
