a = 573×439-434×573-578
a = 251547-248682-578
a = 2865-578
a = 2287
b = {10^3+10^2[10+(5^2-5)]} : 20^2-2^2×2010^0
b = [1000+100(10+25-5)] : 400 - 4 × 1
b = (1000+100×30):400-4
b = (1000+3000):400 -4
b = 4000 : 400 - 4
b = 10 - 4
b = 6
2287 + 6 = 2293 (suma)
2287 - 6 = 2281 (diferenta)
2293 - 2281 = 12
varianta A) este corecta