I need to answer this question about linear equation for homework:

Sally has a total of $3.10 in her pocket in only 10 cent and 20 cent coins. if she had 19 coins altogether, how many if each coin does she have?

i have no idea how to solve these please help :(

Let x = number of 10 cent coins & y = number of 20 cent coins.

x +y = 19 (1)
10x +20y = 310 (2)
10 times (1) gives 10x +10y = 190 (3)
(2) -(3) gives 10y = 120 , so y = 12
x = 7

Therefore there are 7 ten cent coins and 12 twenty cents coins.

Let x be the number of 10 cent coins and y the number of 20 cent coins

x + y = 19 Number of coins
10x + 20y = 310 Values of coins in cents
10x + 10y = 190 10 times first equation
------------------------
.........10y = 120

y = 12, x = 7

Check: 7(10) + 12(20) = 70 + 240 = 310

Let there be "x" 10 cents coins.
Therefore 10x + 20( 19 -x ) = 310
10x + 380 - 20 x = 310
-10x = -70
70 = 10x
7 = x
Answer: 7 of 10 cents coins and 12 of 20 cents coins.