Multiplication boxes and triangles

This task is about completing multiplication number sentences.
 

2      3

4      5      6

7      8      9      10
 
 
Use the numbers above to complete each equation by filling in the boxes and triangles. 
Each number can be used more than once in each equation.
 
a) × × 3 =             18
b) × 2 × =             40
c) 4 × × =             36