finishing off with qsn 1...
y + x dydx = x f(xy) f'(xy)
yx + dydx = f(xy) f'(xy)
I.F. = e∫1x dx = x
so...
y + x dydx = x f(xy) f '(xy)
d(xy) = x f(xy) f '(xy) dx
∫ f '(xy) f (xy) d(xy) = ∫ x dx
ln (f(xy)) = x22 + ln k
or f(xy) = k ex2/2
so answer a...