3p+4s=68 and 3p+7s=92 we can rearrange equation 1 to let 's' be the subject : s=(68-3p)/4. We can then sub this into equation 2 so that there is only one unknown: 3p+7(68-3p)/4=92. Then takeaway p from both sides: 7(68-3p)/4=92-3p. Then multiply by 4: 7(68-3p)= 4(92-3p). The use distributive law on both sides: 476-21p=368-12p. Then rearrange to get 108=9p and the divide by 9 and you will get p=12 Hope this helps!!
