First you have to do the problem in the perenteces, so 21 + 42 = 63. Now we have to do 63 x 3 which is 189. We have to do the second one now so 18 + 12 is 30, and now we times that by 4, so know it is 120. Lastly we add 189 + 120 which gives us an answer of 309.
It is 309.