Rounding the first number, you have
[tex]2.34\approx2.3\approx2[/tex]because the number is rounded down if the digit to the right is less than 5.
Rounding the second number, you have
[tex]6.9\approx7[/tex]because the number is rounded up if the digit to the right is greater than 5.
Therefore, estimating and calculating, you have
[tex]2.34\cdot6.9\approx2\cdot7=14[/tex]