Write two functions with python to perform forward and back substitution.

define a function

# name : forward$\_$subs

# inputs : G $(2$D numpy array$),$ b $(1$d numpy array$)$

# output : x $(1$d numpy array$),$ solution to Gx$=$b

# note $1$ : assume the sizes are compatible

# note $2$ : assume G is square, invertible, and lower triangular

# note $3$ : the computation should be done using for loops

# rather than a built$-$in numpy function

# note $4$ : the function should work for square matrices of any size