The answer is 3f
<span>=<span><span>18f</span>+<span>−<span>15f</span></span></span></span><span>=<span>(<span><span>18f</span>+<span>−<span>15f</span></span></span>)</span></span><span>=<span>3<span>f</span></span></span>
The first one in incorrect , it should be 130 but the rest are correct !
