The total cost of two notebooks is $4.00 x 2 = $<<4*2=8.00>>8.00.
The total cost of two pen $1.50 x 2 = $<<1.5*2=3.00>>3.00.
So, the total amount Rubble spent for all the stuff was $8.00 + $3.00 = $<<8+3=11.00>>11.00.
Therefore, Rubble was left off with $15.00 - $11.00 = $<<15-11=4.00>>4.00.
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