Explanation:
y is easy.
it is the Hypotenuse (baseline) of the small right-angled triangle created by the height (8) of the main triangle, the segment 6 of the main Hypotenuse and y.
so, Pythagoras :
y² = 8² + 6² = 64 + 36 = 100
y = 10
x is a bit more complex.
I think the easiest way to get it is to know that the height of a right-angled triangle to the Hypotenuse is the square root of the product of both segments of the Hypotenuse.
so, if we call the segments of the Hypotenuse a and b with a = 6, we have
x = a + b = 6 + b
height (8) = sqrt(a×b) = sqrt(6b)
therefore,
6b = height² = 8² = 64
b = 64/6 = 32/3 = 10 2/3 = 10.66666666...
so,
x = 6 + 10.66666... = 16.666666666...
round it to what is needed. e.g. 2 positions after the decimal point (hundredths) ? then it would be 10.67