please explain how to solve. i dont understand when to subtract or when to add and why is that.

4. Consider the following chain mechanism: (1) AHHA+H (2) A. B B. + C (3) AH+BAA+D (4) A+BBP (a) Identify the initiation, propagation, and termination steps. (b) Write the rate law for the rate of disappearance of AH,dtd[AH]. Leave in terms of reactive intermediates. (c) Write expressions for the net-rate of reaction of the intermediates, A-and B- dtd[A]= and dtd[B]= ? Appling the steady-state approximation, what are the numerical values of each of these rates. 4 a. (1) initiation; (2)d(3) propagationj (4) Temmination b. dtd[AH]=k1[AH]+k3[AH[LB] c.dtd[A]=k1[A]k2[A]+k3[AH][B]k4[A[B3]=0dtd[B]=k2[A]k3[AH][B3]k4[A][B]=0