a) \(2x\left(3x+5\right)=3x\left(10+2x\right)+15\)
\(\Leftrightarrow6x^2+10x=30x+6x^2+15\)
\(\Leftrightarrow6x^2+10x-30x-6x^2=15\)
\(\Leftrightarrow-20x=15\)
\(\Leftrightarrow x=-0.75\)
b) \(3x\left(x+5\right)-x\left(3x-10\right)+7=0\)
\(\Leftrightarrow3x^2+15x-3x^2+10x+7=0\)
\(\Leftrightarrow25x+7=0\)
\(\Leftrightarrow25x=-7\)
\(\Leftrightarrow x=-0.28\)