The first excersise you have to apply the distributive property,
Multiply,
[tex]2 \times 2c = 4c[/tex]
[tex]2 \times 5 = 10[/tex]
Then solve with the new equation
[tex]3c + 4c + 10 = 3[/tex]
[tex]c = - 1[/tex]
For the second one just try and leave the variable alone,
[tex]d = 571.9[/tex]
In the third equation also apply the distributive property, then leave the variable alone,
[tex]9b - 10 = 6b + 8[/tex]
[tex]3b = 18[/tex]
Then divide,
[tex]b = 6[/tex]
