7.28·3-57 34+13·5 98-23·4+ 24 28·2-13·4

1. $$28 \cdot 3 - 57 = 84 - 57 = 27$$

2. $$34 + 13 \cdot 5 = 34 + 65 = 99$$

3. $$98 - 23 \cdot 4 + 24 = 98 - 92 + 24 = 6 + 24 = 30$$

4. $$28 \cdot 2 - 13 \cdot 4 = 56 - 52 = 4$$

Ответ: 1) 27; 2) 99; 3) 30; 4) 4.