B) (a^2-a)-(3a+a^2) npu a=9,21

Let's simplify the expression \((a^2 - a) - (3a + a^2)\) and then substitute \(a = 9.21\).<br /><br />First, distribute the negative sign in the second term:<br />\[<br />(a^2 - a) - (3a + a^2) = a^2 - a - 3a - a^2<br />\]<br /><br />Next, combine like terms:<br />\[<br />a^2 - a - 3a - a^2 = -4a<br />\]<br /><br />Now, substitute \(a = 9.21\):<br />\[<br />-4a = -4 \times 9.21 = -36.84<br />\]<br /><br />So, the final answer is:<br />\[<br />-36.84<br />\]