5×6÷2= 15 (square centimeter)

fourth

( 18-5-3)×3÷2= 15

Eighth:

They are 43 40 8 respectively.

tenth

3. 14× 16÷2=25. 12

twelve

3×2+5×4

Tell me first, and then think for yourself! Come on! ! ! O(∩_∩)O~