Question

Please help me with this question!

Answer 1

First off, let's convert the percentages to decimal format, so our 77% turns to 77/100 or 0.77, and our 55% turns to 55/100 or 0.55 and so on

now, the sum of both salines, must add up to the 77% mixture, let's say is "y"
so, 11 + 4 = y, and whatever the concentration level is, must also sum up to the mixture's concentration of 77%

anyway   thus

$\bf \begin{array}{lccclll} &amount&concentration& \begin{array}{llll} concentrated\\ amount \end{array}\\ &-----&-------&-------\\ \textit{first sol'n}&11&x&11x\\ \textit{second sol'n}&4&0.55&2.20\\ ------&-----&-------&-------\\ mixture&y&0.77&0.77y \end{array}\\\\ -------------------------------\\\\ \begin{cases} 11+4=y\implies 15=\boxed{y}\\ 11x+2.2=0.77y\\ ----------\\ 11x+2.2=0.77\cdot \boxed{15} \end{cases}$

solve for "x"