Integral of $$$3 \sin{\left(x \right)}$$$

Apply the constant multiple rule $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ with $$$c=3$$$ and $$$f{\left(x \right)} = \sin{\left(x \right)}$$$:

$${\color{red}{\int{3 \sin{\left(x \right)} d x}}} = {\color{red}{\left(3 \int{\sin{\left(x \right)} d x}\right)}}$$

The integral of the sine is $$$\int{\sin{\left(x \right)} d x} = - \cos{\left(x \right)}$$$:

$$3 {\color{red}{\int{\sin{\left(x \right)} d x}}} = 3 {\color{red}{\left(- \cos{\left(x \right)}\right)}}$$

Therefore,

$$\int{3 \sin{\left(x \right)} d x} = - 3 \cos{\left(x \right)}$$

Add the constant of integration:

$$\int{3 \sin{\left(x \right)} d x} = - 3 \cos{\left(x \right)}+C$$

Answer: $$$\int{3 \sin{\left(x \right)} d x}=- 3 \cos{\left(x \right)}+C$$$