Please see the attached problem. Rate is being defined as d[P]/dt, and d[P]/dt = k3[ES]. So the main challenge is expressing [ES]. I applied the steady-state approximation to find [ES] = [E][noparse][/noparse]k1+k-2[ES2] / (k3+k-1+k2[noparse][/noparse]). The other equation I've used is [E]0=[E]+[ES]+[ES2], the E mass balance. But I can't seem to eliminate all of the extra variables doing that alone. What should I do?