We can write an equation based on the information in the problem.
#y=mx+b# is the skeleton for our equation.
We can think of #b# as our starting point, the very least we can be charged. The problem tells us our base fee is #$15.99# and that they add on #$.18# for every additional minute.
So #b# is #15.99#, and #m# is our rate, which is #.18#. Now w just need to figure out where that #48# goes. It can either be the #x# or the #y#.
In math, #x# is the independent variable and #y# is the dependent variable. Those might sound like big, science-y words, but they basically mean that a change is #y# is cause by #x#. In this case, the more minutes are use, the money the phone is charged.
So minutes change money. That means #x# is minutes and #y# is money.
#48# is the number of minutes spent talking,s o we're solving for #y# or money:
#y=15.99+48(.18)#
#y=15.99+8.64#
#y=24.63# or #$24.63#
