Линейные уравнения с одной переменной 2х-7=13 и х+5в=15; 2-х/5-х/15=1/3; 3(х-7)=144

Решите задачу:

$1)2x - 7 = 13 \\ 2x =1 3 + 7 \\ 2x = 20 \\ x = 20 \div 2 \\ x = 10$
$2)x + 5b = 15 \\ x = 15 - 5b$
$3)2 - \frac{x}{5} - \frac{x}{15} = \frac{1}{3} \\ 30 - 3x - x = 5 \\ 30 - 4x = 5 \\ 4x = 30 - 5$
$4x = 25 \\ x = 25 \div 4 \\ x = 6 \frac{1}{4} = 6.25$
$4)3x - 21 = 144 \\ 3x = 144 + 21 \\ 3x = 165 \\ x = 165 \div 3 \\ x = 55$