Recall the trigonometry rule SOH/CAH/TOA (Silly Old Hitler Couldn't Advance His Troops Over Africa).

Label: Draw the triangle and label the sides with Hyp, Opp & Adj.
Choose: Pick which equation to use from SOH/CAH/TOA. In this case, we choose "SOH" because we want to find the opposite side
and we are given the angle and the length of the hypotenuse.
Cover: Using the triangle form of the equation for SOH, cover up what you want to find and write down the expression of what
you see. So opp = sin(angle) x hyp
Substitute: opp = sin(angle) x hyp then becomes opp = sin(30) x 8
Evaluate: opp = 0.5 x 8 = 4cm

Expand: (x+3)(2x+4)