\[\boxed{\mathbf{3.}}\]
\[\textbf{а)}\ 35 + 20 = 55\]
\[54 + 30 = 84\]
\[43 + 40 = 83\]
\[38 + 50 = 88\]
\[11 + 60 = 71\]
\[12 + 70 = 82\]
\[\textbf{б)}\ 20 + 56 = 76\]
\[30 + 64 = 94\]
\[40 + 32 = 72\]
\[50 + 48 = 98\]
\[60 + 13 = 73\]
\[70 + 21 = 91\]