a)\(15.\left(-2\right).\left(-5\right).\left(-6\right)=\left(-30\right).30=\left(-900\right)\)
\(15.\left(-2\right).\left(-5\right).\left(-6\right)\)
\(=\left[15.\left(-2\right)\right].\left[\left(-5\right).\left(-6\right)\right]\)
\(=-30.30\)
\(=-900\)
\(4.7.\left(-11\right).\left(-2\right)\)
\(=28.\left(-11\right).\left(-2\right)\)
\(=\left[28.\left(-2\right)\right].\left(-11\right)\)
\(=\left(-56\right).\left(-11\right)\)
\(=616\)