user: I've been brushing up on my linear algebra and I'm working with matrix operations. I have these two matrices I need to multiply: the first one, matA, contains [[1, 2], [3, 4]] and the second one, matB, contains [[5, 6], [7, 8]]. Could you multiply these two for me? Also, while you're at it, I have this list of numbers [1,2,3,4], and I'm looking to calculate the average. What's the mean of this list?

Available functions:
name: mat_mul
description: Multiplies two matrices.
parameters: type: dict
properties: matA: type: array
description: The first matrix.
items: type: integer
matB: type: array
description: The second matrix.
items: type: integer
required: matA
matB
name: calculate_mean
description: Calculates the mean of a list of numbers.
parameters: type: dict
properties: numbers: type: array
items: type: float
description: The list of numbers.
required: numbers