This exercise wants you to build a linear system of two equations and two unknowns.
To do so, we assign a variable to each of the quantity we want to calculate, so let's call [tex] d [/tex] the cost of one daylily and [tex] s [/tex] the cost of one shrub.
We know that Ashley bought 7 daylilies and 2 shrubs, so she paid
[tex] 7d+2s = 45 [/tex]
Similarly, Lisa spent
[tex] 14d+11s = 174 [/tex]
for 14 daylilies and 11 shrubs.
So, the system is
[tex] \begin{cases}
7d+2s = 45\\
14d+11s = 174
\end{cases} [/tex]
To solve the system, we must manipulate its equations in order to find the value of one particular variables. For example, we can multiply the first equation by 2 to get
[tex] \begin{cases}
14d+4s = 90\\
14d+11s = 174
\end{cases} [/tex]
Now, if you subtract the first equation from the second you have
[tex] 7s = 84 \implies s = 12 [/tex]
So, one shrub costs 12 dollars. We can substitute this value for [tex] s [/tex] in any of the equation, and solve it for [tex] d [/tex]. For example, if we choose the first one we have
[tex] 7d+2s = 7d+24= 45 \implies 7d = 21 \implies d=3 [/tex]
So, one daylily costs 3 dollars.
