Answer :
[tex]\begin{gathered} 1.\text{ a=17} \\ 2.\text{ }b=87 \\ 3.x=10 \\ 4.x=42 \end{gathered}[/tex]
Explanation
Step 1
[tex]\begin{gathered} a+15=32 \\ \text{subtract 15 in both sides} \\ a+15-15=32-15 \\ a=17 \end{gathered}[/tex]Step 2
[tex]\begin{gathered} b-12=75 \\ \text{add 12 in both sides} \\ b-12+12=75+12 \\ b=87 \end{gathered}[/tex]Step 3
[tex]\begin{gathered} 9x=90 \\ we\text{ n}eed\text{ isolate x, so divide both sides by 9} \\ \frac{9x}{9}=\frac{90}{9} \\ x=10 \end{gathered}[/tex]Step 4
[tex]\begin{gathered} \frac{x}{6}=7 \\ \text{Multiply both sides by 6} \\ \frac{x}{6}\cdot6=7\cdot6 \\ x=42 \end{gathered}[/tex]I hope this helps you