substitute the y values.
take everything, divide it by the y coefficient
sub that into the other equasion
gives us 19x/7 = 18.75
19x = 131.25
x ~= 6.91
now we sub the x value into either equasion.
and win!
unsure about your school curriculum, but you generaly get to use a calculator.
if you format it into
ax +by = c
dx +ey = f
your calculator should be able to do it for you