\(a,5^x+5^{x+2}=650\\ \Rightarrow5^x+5^x.25=650\\ \Rightarrow26.5^x=650\\ \Rightarrow5^x=25\\ \Rightarrow5^x=5^2\\ \Rightarrow x=2\)
\(b,3^{x-1}+5.3^{x-1}=162\\ \Rightarrow6.3^{x-1}=162\\ \Rightarrow3^{x-1}=27\\ \Rightarrow3^{x-1}=3^3\\ \Rightarrow x-1=3\\ \Rightarrow x=4\)