The x 2 coefficient of (a+3x) 5 is 8 times of the x coefficient. Find the value of the constant a.

According to binomial theorem, the coefficient of x 2 is c (5,2) * a 3 * (3) 2, and the coefficient of x is c (5,1) * a 4 * (3). A=0.75 can be obtained from the multiple relation equation.