Well just use the formula a^2+b^2=c^2. C squared in this case will be 30, It does not matter whether 24 is a or b^2 since we are still adding them. Now your equation should look like this
a^2+24=30 then….
a^2=30-24
a^2=6
a=square root of 6
Therefore your radius is square root of 6 or x=square root of 6