You mean "four" erasers instead of "for" erasers which i corrected and solved.
Answer: You will pay 102Ghana cedis
Explanation:
a pencil cells at 18 Ghana cedis
Three pencils will cost 3 x 18Ghana cedis=54 Ghana cedis
Also an eraser class at 12 Ghana cedis
Four erasers will cost 4 x 12 =48Ghana cedis
Total amount for three pencils and for erasers =54 Ghana cedis+48Ghana cedis=102Ghana cedis.