angle a = 40.6°
step-by-step explanation:
for any right angle triangle we know the pythagoras theorem reveals
hypotenuse² = height²+base²
by this formula we will calculate the length of hypotenuse
h² = 6²+7²
⇒ h =√36+49 = √85 = 9.22
now from the given triangle sin a = height/ hypotenuse
sin a = 6/9.22 = 0.651
therefore
so angle a = 40.6°