Enter the value of c when the expression 21.2x+c is equivalent to 5.3(4x-2.6)

Super ultra mega important if you can answer this correctly i will give you 100 points but if you don't answer it correctly you'll get a big report. so stay aware and have a nice day!

Need plz been trying to do it for a long time and still haven’t succeeded

Use long division to indentify (12xto the second power+15x-8)divided by 3x