Tolong jawab... Yg no 1,2,3 belum paham soalnya

[tex]1. \: l = \frac{a + b}{2} \times t \\ \\ 330 \: = \frac{a + 19}{2} \times 12 \\ \\ 330 = \: 19a \times 6 \\ \\ 330 = 114a \\ \\ a = \: 330 \div 114 \\ \\ a \: = 2.89 \: cm \\ \\ \\ 2. \: l = \frac{a + b}{2} \times t \\ \\ 199 \: = \frac{19 + b}{2} \times 7 \\ \\ 199 = \frac{19b \times 7}{2} \\ \\ 199= \frac{133b}{2} \\ \\ 199 = 66.5b \\ \\ b = 199 \div 66.5 \\ \\ b = 2.99 \: cm \\ \\ \\ 3. \: l = \frac{a + b}{2} \times t \\ \\ 312 = \frac{28 + 20}{2} \times t \\ \\ 312 = \frac{48}{2} \times t \\ \\ 312 = 24 \times t \\ \\ t = 312 \div 24 \\ \\ t = 13 \: cm \\ \\ \\ 4. \: l = \frac{a + b}{2} \times t \\ \\ = \frac{25 + 26}{2} \times 12 \\ \\ = 51 \times 6 \\ \\ = 306 \: {cm}^{2} [/tex]