exam Maths Puzzle Numerical Ability

Please help me solve for x. I keep getting stuck.
f(x)= x^4+x^2-12.

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exam Other Question

At 3pm a plane leaves London to fly to Madrid which is 1260 miles away. At 4PM a plane leaves Madrid to fly to London. The second plane flies 40 MPH faster than the first plane. If the planes pass one another at 4:30pm, what is the speed of each plane? Here is another one I can not figure out. I am confused on what procedure. Can someone help me.
Multiply the following:

(x/3 + 3/4)(3x/4 - 3/5)