Hi! Please i need your help!. Thank you to those who help and answer correctly

I believe there are 5

Step-by-step explanation:

if there are 4 friends and Mary then that makes 5 people in total.

19.side- angle- side

20. angle- side- angle

step-by-step explanation:

solution:

→c= a b , that is product of a and b is possible only when when a is m × n matrix and b is n × p matrix.

that is, number of columns of a= number of rows of b.

so, size of matrix , c= a b is , if a = (m × n)matrix

b= (n × p)matrix

then a b = [ (m × n)matrix] ×[   (n × p)matrix ]

→→c= a b= [m × p ] matrix

→→size of product a b will be equal to = number of rows of a × number of columns of b