These tiles represent the expression 3+6x+1.

To determine an expression equivalent to \(3 + 6x + 1\), let's simplify the original expression.

1. Start by adding the constant terms: \[ 3 + 1 = 4 \]

2. Then, combine it with the term involving \(x\): \[ 4 + 6x \]

So, \(3 + 6x + 1\) simplifies to \(4 + 6x\).

Therefore, the expression equivalent to \(3 + 6x + 1\) is \(4 + 6x\).