\(\Rightarrow5^2\cdot5^{x+3}=5^6\\ \Rightarrow5^{x+3}=5^4\\ \Rightarrow x+3=4\\ \Rightarrow x=1\)
\(25.5^{x+3}=5^6\)
\(\Rightarrow5^2.5^{x+3}=5^6\)
\(\Rightarrow5^{x+3}=5^6:5^2\)
\(\Rightarrow5^{x+3}=5^4\)
\(\Rightarrow x+3=4\)
\(\Rightarrow x\) \(=4-3\)
\(\Rightarrow x\) \(=1\)