It would be 4.9 because you would use a^2+b^2=c^2. The hypotenuse is always c^2. Write this our as
x^2+5^2=7^2.
Break these down so its
x^2+25=49
you want the x alone so you'll subtract 25 from both sides which in the end is
x^2=24
You want to get rid of the exponent so you place √ in front of 24. In the end it looks like
x=√24 Plug it into a calculator and it'll give you 4.89. Round it and it'll give you answer A (4.9cm)