Quick plz asap marking brainliest for first answer as long as you include steps ! solve the system of equations using linear combination. a + c = 12 4a + 7.5c = 72.5 linear combination method ! not substitution or elimination

a=2.48

c=9.52

Step-by-step explanation:

a+c=12

4a+7.5c=72.5 Given

a+c=12

-4a-7.5c=-72.5 multiply the equation by negative 1

-3a-6.5c=-60.5 simplify

-3a=-60.5+6.5c add 6.5c to both sides

a=-20.17+2.17c divide it by 3

now you would take that equation and plug it into an equation you already have since you have something to plug in for a, the easiest one to do is a+c=12

(-20.17+2.17c)+c=12 plug in the equation

-20.17+3.17c=12 simplify by solving for c

3.17c=30.17 add 20.17 to both sides

c=9.52 divide both sides by 3.17

now since you have found c, you can plug it in to you equation to solve for a now (use the ones from the second step).  I am using the equation a+c=12.

a+9.52=12 plug in the variable and solve for a

a=2.48 subtract 9.52 to both sides

a=2.48

c=9.52

stops on an even number.

if gloria has "carry over" minutes, (that is, any minutes paid for but not used in a month can be applied to her payment for minutes in the next month,) her total usage for the three months is: total minutes = 320 + 243 + 489 = 1052 minutes number of 200 minute blocks = 1052/200 = 5 r52 (that is 5 with a remainder of 52) rounding up the number of 200 minute blocks gives her usage for the three months as 6 blocks. the cost for six blocks is 6 x $25 = $150 she also has 200 - 52 or 148 carry over minutes if gloria pays each month and unused minutes are lost, applying the rounding up procedure to each month gives: first month usage of 320 minutes rounds up to 2 blocks of 200 minutes for a payment of 2 x $25 = $50 second month usage of 243 minutes rounds up to 2 blocks of 200 minutes for a payment of 2 x $25 = $50 third month usage of 489 minutes rounds up to 3 blocks of 200 minutes for a payment of 3 x $25 = $75 total payments for the three months are $50 + $50 + $75 = $175 get the plan with carry over minutes!