Shota tried to subtract two polynomials. His work is shown below: \begin{aligned} &\phantom{=}(12a^2+3ab+4b^2)-(7 a^2-5ab+b^2) &=12a^2+3ab+4b^2-7a^2+5ab-b^2&a mp;\text{Step }1 &=(12+3)a^3+(3+4)b^3+(-7+5)a^3+ (5-1)b^3&\text{Step }2 &=15a^3+7b^3-2a^3+4b^3&\tex t{Step }3 \end{aligned} ​ =(12a 2 +3ab+4b 2 )−(7a 2 −5ab+b 2 ) =12a 2 +3ab+4b 2 −7a 2 +5ab−b 2 =(12+3)a 3 +(3+4)b 3 +(−7+5)a 3 +(5−1)b 3 =15a 3 +7b 3 −2a 3 +4b 3 ​ Step 1 Step 2 Step 3 ​