Bayesian networks problem - Find the probability of rain gives grass wet given conditional probability values

Question

Problem statement Rain influences sprinkler usage. Rain and sprinkler influences whether grass is wet or not. What is the probability that rain gives grass wet?

Edit: The problem statement is verbatim from my question paper. I understand "rain gives grass wet" doesn't make much sense. I inferred it as "grass it wet and it rained" but I did not edit it since I'm not entirely sure.

Conditional probability values

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I solved it thus:

P(G,R)=(P(G|!S,R).P(!S|R) + (P(G|S,R).P(S|R)).P(R)
        =((0.99*0.01)+(0.8*0.99))*0.2

Can someone tell me if I am right or explain why I am wrong?