Here, we want to open up the bracket. We simply multiply each of the term in the bracket by the term outside the bracket.
A key information here is that;
[tex]\begin{gathered} x^2\text{ }\times x^3=x^{2+3}=x^5 \\ \text{and not x}^{2\times3}=x^6 \end{gathered}[/tex]We proceed as follows;
[tex]\begin{gathered} 3x^2(5^{}x^3\text{ + 6x - 2)} \\ \\ =15x^5+18x^3-6x^2 \end{gathered}[/tex]