To evaluate the expression \(3x + 5.7y\) for \(x = 1.2\) and \(y = 5\), we can substitute the values of \(x\) and \(y\) into the expression:
\[ 3(1.2) + 5.7(5) \]
Calculating each term:
- \(3(1.2) = 3.6\)
- \(5.7(5) = 28.5\)
Now, adding these results together:
\[ 3.6 + 28.5 = 32.1 \]
Thus, the value of the expression is \(32.1\).