Let, number of small and big pumpkin are x and y.
So, mathematical equation is given by :
x + y = 29 ...1)
3x + 5y = 105 ...2)
Putting value of x from equation 1 to equation 2, we get :

So, x = 20
Therefore, number of small and large pumpkins are 20 and 9 respectively.
Hence, this is the required solution.