8×{[(7+4)×2]-[(11-7)×4]}

Solve in the brackets first. then the rest so...
8*{[(7+4)*2]-[(11-7)*4]}      <-- this is the starting equation
8*{[(11)*2]-[(4)*4]}       <-- here i solved the inner most brackets which was 7+4 and 11-7
8*{[22]-[16]}    <-- then i multiplied 11 by 2 to get 22 and 4 by 4 to get 16
8*{6}    <-- here i subtracted 16 from 22 to get 6
48     < and then the answer which i got by multiplying 6 and 8
**note: keep BEDMAS/BODMAS in your mind. u solve the inner most brackets first and then you move outside. 
48 is the answer
hope it helped :)

Idrk but i think u should figure out the n dia n then the units it will make it way more easier