Since we know that t = 3.4 you put 3.4 where the t is.
2 (36 - 4 × 3.4) So what you do first is multiply 4 and 3.4 which gives you 13.6
2 (36 - 13.6) then you subtract 36 and 13.6 which gives you 22.4
2 (22.4) then you multiply 2 and 22.4 which is 44.8.
So your answer is 44.8
I hope that helped!