The question can be broken into two steps,
1) dy/dx is asking to differentiate y=x3+5x+3 with respect to x
Differentiating we multiply by the current power and lower this powers value by 1. ( Constants differentiate to nothing )
i.e x3 goes to 3x2
dy/dx= 3x2+5
2) Next we need to find the value of dy/dx when x=3 done simply by substituting all x's in the equation by 3
dy/dx= 3*(3)2 + 5 = 32