Answer:
4.383
Explanation:
Pythagoras
a² + b² = c²
with c being the baseline of the rectangular triangle (the line opposite to the 90 degree angle).
so, in our example here c=6.5cm, a=QR, b=4.8cm
a² = c² - b² = 6.5² - 4.8² = 19.21
a = sqrt(19.21) = 4.383