How many acute angles are formed by the 4 intersecting lines shown? [asy] import olympiad; size(150); pair a=(0,0), b = 4*dir(0), c=4*dir(40),d=4*dir(100),e=4*dir(15 0),f=4*dir(180),g=4*dir(220),h=4*di r(280),i=4*dir(330); dot(a, red); draw(a--b, endarrow); draw(anglemark(b, a,c,20),black); label("$40^\circ$",anglemark(b, a,c),4*dir(20)); draw(a--c, endarrow); draw(a--d, endarrow); draw(a--e, endarrow); draw(anglemark(d, a,e,20),black); label("$50^\circ$",anglemark(d, a,e),4*dir(120)); draw(a--f, endarrow); draw(a--g, endarrow); draw(a--h, endarrow); draw(anglemark(g, a,h,20),black); label("$60^\circ$",anglemark(g, a,h),4*dir(250)); draw(a--i, endarrow); [/asy]?