a) x+9=18 b) x-1=-8 3y-8=13 12x-10=5x+11

a) To solve the equation $x+9=18$, we need to isolate the variable $x$ on one side of the equation. <br /><br />Step 1: Subtract 9 from both sides of the equation.<br />$x+9-9=18-9$<br /><br />Step 2: Simplify the equation.<br />$x=9$<br /><br />Therefore, the solution to the equation $x+9=18$ is $x=9$.<br /><br />b) To solve the equation $x-1=-8$, we need to isolate the variable $x$ on one side of the equation.<br /><br />Step 1: Add 1 to both sides of the equation.<br />$x-1+1=-8+1$<br /><br />Step 2: Simplify the equation.<br />$x=-7$<br /><br />Therefore, the solution to the equation $x-1=-8$ is $x=-7$.<br /><br />c) To solve the equation $3y-8=13$, we need to isolate the variable $y$ on one side of the equation.<br /><br />Step 1: Add 8 to both sides of the equation.<br />$3y-8+8=13+8$<br /><br />Step 2: Simplify the equation.<br />$3y=21$<br /><br />Step 3: Divide both sides of the equation by 3.<br />$\frac{3y}{3}=\frac{21}{3}$<br /><br />Step 4: Simplify the equation.<br />$y=7$<br /><br />Therefore, the solution to the equation $3y-8=13$ is $y=7$.<br /><br />d) To solve the equation $12x-10=5x+11$, we need to isolate the variable $x$ on one side of the equation.<br /><br />Step 1: Subtract 5x from both sides of the equation.<br />$12x-10-5x=5x+11-5x$<br /><br />Step 2: Simplify the equation.<br />$7x-10=11$<br /><br />Step 3: Add 10 to both sides of the equation.<br />$7x-10+10=11+10$<br /><br />Step 4: Simplify the equation.<br />$7x=21$<br /><br />Step 5: Divide both sides of the equation by 7.<br />$\frac{7x}{7}=\frac{21}{7}$<br /><br />Step 6: Simplify the equation.<br />$x=3$<br /><br />Therefore, the solution to the equation $12x-10=5x+11$ is $x=3$.