Answer:
Step-by-step explanation:
(a + b)²=a²+2ab+b²
(3x+3y)²= (3x)²+2*3x*3y+(3y)²
=9x² + 18xy + 9y²
=9x² + 9y² + 18xy
= 9*(x²+y²) +18xy
=9*25 + 18*12
=225 + 216
=441
