\(a,\left(2x+5\right):3-121:11=4\)
\(\left(2x+5\right):3-11=4\)
\(\left(2x+5\right):3=4+11\)
\(\left(2x+5\right):3=15\)
\(2x+5=15.3\)
\(2x+5=45\)
\(2x=45-5\)
\(2x=40\)
\(x=40:2\)
\(x=20\)
Vậy \(x=20\)
\(b,\left(4x+1\right)^3=125\)
\(\left(4x+1\right)^3=5^3\)
\(\Rightarrow4x+1=5\)
\(4x=5-1\)
\(4x=4\)
\(x=4:4\)
\(x=1\)
Vậy \(x=1\)