[plt-scheme] matrix algebra

i m trying to write a function that implements matrix algebra . I saw it on the book exexcise  but i think i need a help coz i m very new on scheme

Example
(1 - 1/3) +[ 2     -1/2] * [ -8     -1/2    3/25 ] +[2       3      -1]  = [-85/9   -34/15   -408/575   ]
                [ 7/3   5   ]   [  7/3    1/5    -9/23]   [1/2    1/3   -1] = [-25/6     2/9      -3653/1725]



                     >  (mateval  ' (+ (* (- 1 ( 1 3))
                                                      ( ( 2 ( -1 2))     ( (7 3) 5) )
                                                      ( (-8 (-1 2)  (3 25) )  ( (7 3) (1 5) (-9 23) ) ) )
                                                  ( ( 2 3 -1)  ( ( 1 2)  (1 3) -1 ) )  ) )
the result
                > ( ( (- 85 9)  (34 15)  (-408 575) )  ( ( -25 6)  (2 9)  (-3653 1725) ) )

 the first expression  , (1 - 1/3) , is not matrix but constant
and
          (  1  3 )  is representing  1/3
           (-  1  2)  is representing -1/2  i mean this is the rational representing form



help me pls

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